Chapter 36

Drum Brake Systems Theory

Learning Objectives

After reading this chapter, you will be able to:

• 36-01 Describe drum brake fundamentals.
• 36-02 Describe the types of drum brake systems.
• 36-03 Describe brake drums and backing plates.
• 36-04 Describe wheel cylinders.
• 36-05 Describe brake shoes and lining.
• 36-06 Describe drum brake springs.
• 36-07 Describe drum brake self-adjusters and parking brake operation.

ASE Education Foundation Tasks

The following ASE Education Foundation Automobile Accreditation Tasks are covered in this chapter:

• VA4 Identify brake system components and configuration.

Readings and Preparation

• Review all instructional materials, including the chapter in Fundamentals of Automotive Maintenance and Light Repair, Second Edition, and all related presentation support materials.

Support Materials

• Lecture PowerPoint presentation, including all Skill Drills

Pre-Lecture

• You Are the Automotive Technician
  • A progressive case study that encourages critical thinking skills.
  • Direct students to read the “You Are the Automotive Technician” scenario found at the beginning of each chapter.
  • Group Activity: Direct students to review the discussion questions at the end of the scenario and prepare a response to each question. Facilitate a class discussion centered on the questions.
  • Homework Assignment: Ask students to turn in their comments on the questions.
• Teaching Tip: Explain to students how this material applies to the workplace. Provide an example of a situation to make it relevant and meaningful. How does it fit into the broader picture? Is it building on something they already know? Will it help them master a skill? Students need to understand that what we are teaching is of importance on the job. This can be done by describing interesting drum brake system repairs you have experienced. You can also have students complete the online pre-test for this chapter in the CDX online system. This will help them understand what they do and do not know about drum brake systems.

Lecture

36-01 Describe drum brake fundamentals.

• Brake drums are bolted to the vehicle’s axle flange by the lug nuts.
• The main components of the drum brake system are the brake drum, backing plate, wheel cylinder, brake shoe, springs and clips, automatic brake self-adjuster, and parking brake mechanism.
• Operation: When the brake pedal is depressed, a pushrod transfers the force to the master cylinder that converts the brake pedal force into hydraulic pressure that is transferred to the wheel cylinders, which apply force to the brake shoes.
• Drum brakes are self-energizing. This means they can increase the force with which they are applied.
• Drum brakes exhibit servo action, which means that one brake shoe, when activated, applies an increased activating force to the other brake shoe.

36-02 Describe the types of drum brake systems.

• There are three main types of drum brake systems: twin leading shoe, leading/trailing shoe (also called single leading shoe), and duo-servo.
• All three types are self-energizing in at least one direction.
• The least common are twin leading shoe drum brake systems that use two single piston wheel cylinders. Each wheel cylinder activates one of the brake shoes. The brakes shoes are arranged in a leading shoe (self-energizing) configuration, which gives very good stopping power in the forward direction.
• The leading/trailing shoe drum brake systems are very common on the rear wheels of front-wheel drive vehicles. They use a single wheel cylinder with two pistons (double-acting wheel cylinder) and each piston operates one of the brake shoes; this arrangement makes one shoe a leading shoe and the other a trailing shoe.
• Duo-servo drum brake systems use servo action in both the forward and reverse directions and use a single wheel cylinder with two pistons (double-acting wheel cylinder).

36-03 Describe brake drums and backing plates.

• Drum brakes function to apply the brake shoes, release the brake shoes, and adjust the brake shoes.
• Brake drums are usually made from cast iron and provide the rotating friction surface that the brake lining contacts.
• Brake drums are machined to a specified diameter by the manufacturer which is called its standard diameter.
• Brake drums can have an integrated hub, called a hub-style drum, or a separate hub called a hubless-style drum.
• All of the brake unit components except the brake drum are mounted on the backing plate; the backing plate is bolted to the vehicle axle housing or knuckle.
• One of the most important components of the backing plate is the anchor pin (or anchor block); the anchor pin must be able to take all the braking force when the brakes are applied.
• The inside surface of the backing plate has flat or raised brake shoe contact pads stamped into it.

36-04 Describe wheel cylinders.

• The wheel cylinder converts hydraulic pressure from the master cylinder into mechanical force that pushes the brake linings against the inside of the brake drum.
• The wheel cylinder is located inside the brake drum and is either bolted or firmly clipped to the backing plate.
• Wheel cylinders usually contain a cylinder housing, one or two pistons, a lip seal for each piston, a spring and expander set, a dust boot for each open end of the cylinder, a pushrod for each piston, and a bleeder screw.
• Wheel cylinders come in different configurations and are either single acting or double acting.
• Single-acting cylinders use a single piston; double-acting cylinders use two pistons opposite each other.

36-05 Describe brake shoes and lining.

• The drum brake system uses metal brake shoes.
• The metal brake shoes have friction material called linings attached to them.
• The composition of the lining material affects brake operation.
• The Society of Automotive Engineers has adopted codes to rate the coefficient of friction of brake lining materials.
• Brake lining materials include non-asbestos organic (NAO) materials, low-metallic NAO materials, semi-metallic materials, and ceramic materials.
• The terms “primary” and “secondary” refer to the brake shoes in a duo-servo brake system. The primary shoe goes toward the front of the vehicle, and the secondary shoe goes toward the rear.

36-06 Describe drum brake springs.

• Different types of springs used in drum brakes are return, hold-down, and specialty.
• Return springs retract the brake shoes when the driver releases the brake pedal.
• Hold-down springs hold the brake shoes against the backing plate; they can be coil springs in combination with a spring retainer and a pin, sometimes referred to as a brake nail.
• Specialty springs are used to return links and levers on the parking brake system or the self-adjuster mechanism; they can be of all different shapes and sizes.

36-07 Describe drum brake self-adjusters and parking brake operation.

• A self-adjuster must be capable of maintaining proper shoe-to-drum clearance.
• There are three types of self-adjusters: manually adjusted threaded star wheel assembly; automatically adjusted star wheel brake adjuster; and automatically adjusted ratchet-style adjuster.
• Drum parking brake systems mechanically apply the regular service brake shoes.
• It is easier to generate the force needed to apply them mechanically than it is to apply disc brakes.
• The parking brake cable attaches to the bottom of the parking brake actuating lever in the drum brake assembly, and the other end of the lever is attached to the top end of one of the brake shoes. A strut rod runs from near the top of the actuating lever to the other brake shoe.
• When the cable is pulled, the lever pivots on the strut rod, which pushes the top of the brake shoe rearward and the strut rod forward. This results in the brake shoes being forced apart and against the drum.

Post-Lecture

This section contains various student-centered end-of-chapter activities designed as enhancements to the instructor’s presentation. As time permits, these activities may be presented in class. They are also designed to be used as homework activities.

1. Direct students to read and individually answer the question sets located in the Wrap-Up section at the end of each chapter. Allow approximately 10–20 minutes for this part of the activity.
2. Facilitate a class review and discussion of the answers, allowing students to correct responses as may be needed. Use the answers noted in the Answer Key to assist in building this review.
3. You may wish to ask students to complete this activity on their own and turn in their answers on a separate piece of paper.

Review Questions

This question set is designed to assist students in understanding the chapter content by asking knowledge-based comprehension questions.

1. Which of the following is true about drum brakes?
   1. They are generally expensive to manufacture.
   2. They are more resistant to overheating.
   3. They are easier to adapt a parking brake to.
   4. They don’t require removal of the drum to inspect linings.

2. What is the purpose of the wheel cylinder?
   1. To support the brake shoes and hardware.
   2. To self-adjust the brakes to compensate for wear.
   3. To form the braking surface for the brake linings.
   4. To push the brake shoes into contact with the drums.

3. What type of drum system is most likely to be found on the rear of a modern front-wheel drive vehicle?
   1. Twin leading shoe
   2. Leading/trailing shoe
   3. Duo-servo
   4. Non-anchored

4. Which type of drum brake design is very efficient at braking in forward, but the least effective in reverse?
   1. Duo-servo
   2. Leading/trailing shoe
   3. Double-anchor
   4. Twin leading shoe

5. A drum with a minimum thickness specification of 10.060″ is measured at 10.070″. Which of the following is most true?
   1. The drum can be machined another 0.010″.
   2. The drum should be inspected and machined.
   3. The drum can be reused if there are no grooves.
   4. The drum must be replaced.

6. How is a wheel cylinder bleeder screw sealed?
   1. With piston seals
   2. With a bleeder O-ring
   3. With a tapered seat
   4. With a bleed passage lip seal

7. In a duo-servo drum brake system, in what location does the primary shoe belong?
   1. Toward the front of the vehicle
   2. On the driver’s side of the vehicle
   3. On the passenger side of the vehicle
   4. Toward the rear of the vehicle

8. What is the most likely condition that would cause brake shoes to click?
   1. The brake shoes are worn to metal on metal.
   2. There is excessive dust in the brake drum.
   3. The brake shoes have worn grooves in the backing plate.
   4. The brake shoes are nearing minimum thickness.

9. All of the following are examples of typical drum brake springs, EXCEPT:
   4. hold-down.

10. When were manufacturers required to integrate self-adjusting devices into their drum brakes?
    1. 1968
    2. 1977
    3. 1986
    4. 2000

ASE Technician A/Technician B Style Questions

This question set is designed to assist students in gaining a further understanding of and familiarity with ASE Technician A/Technician B questions.

1. Drum brakes are being discussed. Technician A states that long downhill grades or heavy use can overheat drums. Technician B states that since drum brakes have more material, they are more resistant to overheating than disc brakes. Who is correct?
   1. Technician A
   2. Technician B
   3. Both A and B
   4. Neither A nor B

2. A brake repair is being discussed. Technician A states that drum brakes have less moving parts and are easier to replace than disc brakes. Technician B states that drum brakes that are misadjusted will have a low brake pedal height. Who is correct?
   1. Technician A
   2. Technician B
   3. Both A and B
   4. Neither A nor B

3. Rear drum brake types are being discussed. Technician A states that a duo-servo system benefits from servo action in forward only. Technician B states that the leading/trailing shoe design produces maximum braking in forward only, so it is commonly found on heavy duty trucks. Who is correct?
   1. Technician A
   2. Technician B
   3. Both A and B
   4. Neither A nor B

4. Drum brakes are being discussed. Technician A states that direct road spray to the brake shoes is prevented by a labyrinth seal in between the drum and backing plate. Technician B states that the shoe to backing plate contact pad should be lightly greased during a brake service. Who is correct?
   1. Technician A
   2. Technician B
   3. Both A and B
   4. Neither A nor B

5. A wheel cylinder is being discussed. Technician A states that the wheel cylinder can be bolted or firmly clipped to the backing plate. Technician B states that most wheel cyl­inders are equipped with one piston and two bleeders. Who is correct?
   1. Technician A
   2. Technician B
   3. Both A and B
   4. Neither A nor B

6. A wheel cylinder is being discussed. Technician A states that if the cylinder bore surface in a wheel cylinder is pit­ted, it should be replaced rather than honed. Technician B states that the purpose of a dust boot is to keep brake dust and moisture away from the piston and cylinder. Who is correct?
   1. Technician A
   2. Technician B
   3. Both A and B
   4. Neither A nor B

7. Brake shoes are being discussed. Technician A states that some brake shoes have lining riveted to the backing and others are bolted. Technician B states that it is a common mistake for new technicians to install both primary shoes on one side of the vehicle, and both secondary shoes on the other side. Who is correct?
   1. Technician A
   2. Technician B
   3. Both A and B
   4. Neither A nor B

8. Drum brake springs are being discussed. Technician A states that it is a good idea to leave one side of the vehicle together for reference while the first side is finished since the spring locations can be confusing. Technician B states that the return springs are generally soft and easy to install by hand. Who is correct?
   1. Technician A
   2. Technician B
   3. Both A and B
   4. Neither A nor B

9. A vehicle with drum rear brakes is being discussed. Techni­cian A states that the self-adjusting mechanism often works to take up slack when stopping in reverse or by applying the parking brake. Technician B states that self-adjusters lengthen over time as the brake shoe linings wear. Who is correct?
   1. Technician A
   2. Technician B
   3. Both A and B
   4. Neither A nor B

10. A parking brake is being discussed. Technician A states that the parking brake typically applies the rear drum brakes hydraulically. Technician B states that drum brakes require less force to apply as a parking brake than disc brakes because of their self-energizing action. Who is correct?
    1. Technician A
    2. Technician B
    3. Both A and B
    4. Neither A nor B

Assignments

• Review all materials from this chapter and be prepared for a chapter quiz to be administered (date to be determined by instructor).
• Direct students to read the next chapter in Fundamentals of Automotive Maintenance and Light Repair, Second Edition as listed on your syllabus to prepare for the next class session.

Chapter 35

Servicing Disc Brakes

Learning Objectives

After reading this chapter, you will be able to:

• 35-01 Describe disc brake diagnosis.
• 35-02 Perform caliper and brake pad service.
• 35-03 Measure and replace disc brake rotors.
• 35-04 Refinish disc brake rotors.
• 35-05 Inspect, replace, and torque lug nuts and studs.

ASE Education Foundation Tasks

The following ASE Education Foundation Automobile Accreditation Tasks are covered in this chapter:

• IIIE4 Inspect and replace drive axle wheel studs.
• VA2 Describe procedure for performing a road test to check bfake system operation, including an anti-lock brake system (ABS).
• VA3 Install wheel and torque lug nuts.
• VD1 Remove and clean caliper assembly; inspect for leaks and damage/wear; determine necessary action.
• VD2 Inspect caliper mounting and slides/pins for proper operation, wear, and damage; determine necessary action.
• VD3 Remove, inspect, and/or replace brake pads and retaining hardware; determine necessary action.
• VD4 Lubricate and reinstall caliper, brake pads, and related hardware; seat brake pads and inspect for leaks.
• VD5 Clean and inspect rotor and mounting surface, measure rotor thickness, thickness variation, and lateral runout; determine necessary action.
• VD6 Remove and reinstall/replace rotor.
• VD7 Refinish rotor on vehicle; measure final rotor thickness and compare with specification.
• VD8 Refinish rotor off vehicle; measure final rotor thickness and compare with specification.
• VD9 Retract and re-adjust caliper piston on an integral parking brake system.
• VD10 Check brake pad wear indicator; determine necessary action.
• VD11 Describe importance of operating vehicle to burnish/break-in replacement brake pads according to manufacturer’s recommendation.

Readings and Preparation

• Review all instructional materials, including the chapter in Fundamentals of Automotive Maintenance and Light Repair, Second Edition, and all related presentation support materials.

Support Materials

• Lecture PowerPoint presentation, including all Skill Drills

Pre-Lecture

• You Are the Automotive Technician
  • A progressive case study that encourages critical thinking skills.
  • Direct students to read the “You Are the Automotive Technician” scenario found at the beginning of each chapter.
  • Group Activity: Direct students to review the discussion questions at the end of the scenario and prepare a response to each question. Facilitate a class discussion centered on the questions.
  • Homework Assignment: Ask students to turn in their comments on the questions.
• Teaching Tip: Explain to students how this material applies to the workplace. Provide an example of a situation to make it relevant and meaningful. How does it fit into the broader picture? Is it building on something they already know? Will it help them master a skill? Students need to understand that what we are teaching is of importance on the job. This can be done by describing interesting disc brake system repairs you have experienced. You can also have students complete the online pre-test for this chapter in the CDX online system. This will help them understand what they do and do not know about servicing disc brake systems.

Lecture

35-01 Describe disc brake diagnosis.

• Disc brake diagnosis starts with understanding the customer’s concern.
• Once the customer concern has been verified, research the concern in the service information and TSBs and create a testing plan.
• Disc brake testing can include visual inspection of brake fluid level and condition, removal of the wheels for brake units for inspection, or measurement of the thickness variation and runout of the rotors.

35-02 Perform caliper and brake pad service.

• Caliper and brake pad service includes removing the caliper and inspecting the caliper mountings, slides, and pins; inspecting brake pad wear indicators; checking brake pads, inspecting the caliper assembly; and retracting and readjusting pistons on an integrated parking brake caliper.
• Clean caliper mountings and slides/pins thoroughly, and inspect them closely for excessive wear.
• The wear indicator system could be a scratcher type or a sensor type. If the scratcher or sensor is contacting the brake rotor, then the brake pads will need to be replaced; if not in contact, then the brake pad thickness will be measured.
• A simple visual inspection along with a measurement of the lining thickness is usually adequate, but if there are customer concerns with the brakes, it may be necessary to remove the pads for a more detailed inspection.

35-03 Measure and replace disc brake rotors.

• Rotors need to be inspected for conditions that would render them useless. One of the most common is excessive wear; another issue is hot spots on the friction surface of the rotor.
• For rotors to function properly, they also need to be within specifications; the three main measurements for disc brake rotors are minimum thickness, lateral runout, and thickness variation.
• Rotors that are too thin experience brake fade sooner than thicker rotors do.
• Excessive thickness variation causes brake pedal pulsation, and excessive lateral runout tends to cause the steering wheel to shimmy when braking.

35-04 Refinish disc brake rotors.

• Rotors need to be refinished when they have excessive runout, thickness variation, or grooving. Rotors can be refinished while on the vehicle or off the vehicle.
• On-vehicle refinishing is preferred by most manufacturers because it minimizes runout issues between the hub and rotor.
• Refinishing a rotor while it is off the vehicle is a bit different than on-vehicle refinishing; most hub-style rotors use the bearing races to center and drive the rotor on the lathe spindle.
• Off the vehicle, hubless rotors are centered in one of two ways.
• Composite hubless rotors use a special adapter which drives the rotor from the center hole while clamping it firmly between solid plates.

35-05 Inspect, replace, and torque lug nuts and studs.

• Wheel studs need to be replaced when they become damaged, that is, when they become stretched, broken off, or cross-threaded due to improper installation.
• There are two primary methods of replacing lug studs: the drawing-in method and the hydraulic press method.
• The drawing-in method uses the lug nut to draw the wheel stud into the flange.
• The hydraulic press method uses a press to force the wheel stud into the flange until it bottoms out and requires the flange to be removed from the vehicle.
• Overtightening the lug nuts can cause the wheel studs to break and can cause warpage of the rotors; undertightening can lead to loosening of the lug nuts.
• Lug nuts should be tightened to the proper torque, in the specified sequence.
• When installing lug nuts, the weight should be off the vehicle and the lug nuts should easily center the wheel on the hub.

Post-Lecture

This section contains various student-centered end-of-chapter activities designed as enhancements to the instructor’s presentation. As time permits, these activities may be presented in class. They are also designed to be used as homework activities.

1. Direct students to read and individually answer the question sets located in the Wrap-Up section at the end of each chapter. Allow approximately 10–20 minutes for this part of the activity.
2. Facilitate a class review and discussion of the answers, allowing students to correct responses as may be needed. Use the answers noted in the Answer Key to assist in building this review.
3. You may wish to ask students to complete this activity on their own and turn in their answers on a separate piece of paper.

Review Questions

This question set is designed to assist students in understanding the chapter content by asking knowledge-based comprehension questions.

1. What can cause brake vibration and pulsations that are considered normal?
   1. ABS operation
   2. Rotor parallelism
   3. Rotor surface finish
   4. Strut rod bushing play

2. What concern is often the first indication that brake pads are worn below specification?
   1. Grabbing brakes
   2. Pulling brakes
   3. Dragging brakes
   4. Noisy (squealing) brakes

3. What will likely happen if brake calipers are installed on the wrong side of the vehicle?
   1. The ABS will activate at inappropriate times.
   2. The brakes will grind constantly.
   3. The brakes will not bleed properly.
   4. The caliper slide pins will bend.

4. What is the proper procedure to retract the pistons on most integrated parking brake calipers?
   1. Compress the piston with a C-clamp being careful not to damage the piston.
   2. Rotate the piston using a special tool that engages the slots or holes on the face.
   3. Release parking brake cable tension and push the piston in by hand.
   4. Cycle the ignition three times with the parking brake applied.

5. What are the three main rotor measurements?
   1. Lateral runout, end play, and thickness variation
   2. Thickness variation, minimum thickness, and maximum diameter
   3. Force variation, maximum diameter, and lateral runout
   4. Minimum thickness, lateral runout, and thickness variation

6. If a rotor is 0.040″ thicker than the minimum thickness, how much metal can commonly be machined off each side before it should be discarded?
   1. 040″
   2. 020″
   3. 010″
   4. 005″

7. When refinishing rotors on the vehicle why should the cut­ting depth not be less than 0.004″?
   1. Too shallow of a cut will overheat the tip of the cutting bit.
   2. A shallow cut will leave a directional finish.
   3. Cutting less than 0.004″ will cause the rotors to chatter.
   4. It will cause hot spots in the rotors.

8. What may happen if the wrong lever is moved during rotor machining?
   1. Excessive lateral runout will warp the rotor and bend the lathe arbor shaft.
   2. The lathe will rotate backward causing the rotor to be machined backward.
   3. The lathe will flash a warning light and a buzzer will sound.
   4. The lathe will feed in the wrong direction cutting a deep groove in the rotor surface.

9. What is burnishing?
   1. Centering the wheel on the hub with tapered lug nuts.
   2. Torqueing the lug nuts so the rotors do not warp.
   3. The transfer of lining material to the rotor evenly.
   4. Performing four ABS stops to heat the rotors rapidly.

10. What is used to draw in the wheel stud using the drawing-in method?
    1. A wheel stud puller
    2. Vise grip pliers
    3. A brass hammer
    4. A lug nut and washers

ASE Technician A/Technician B Style Questions

This question set is designed to assist students in gaining a further understanding of and familiarity with ASE Technician A/Technician B questions.

1. Technician A says that steering and suspension problems may be misdiagnosed as brake issues. Technician B says that professional technicians can be personally held liable for the quality of their brake service and repairs. Who is correct?
   1. Technician A
   2. Technician B
   3. Both A and B
   4. Neither A nor B

2. Technician A says that disc brake vibrations are commonly caused by restricted brake lines or hoses. Technician B says that grabbing brakes could be caused by fluid leaking onto the Who is correct?
   1. Technician A
   2. Technician B
   3. Both A and B
   4. Neither A nor B

3. Technician A says that a dial indicator is used to measure the thickness of the brake pad linings. Technician B says that a bench brake lathe is used to machine drums and rotors. Who is correct?
   1. Technician A
   2. Technician B
   3. Both A and B
   4. Neither A nor B

4. Technician A says that on some vehicles the inboard pad is different from the outboard pad. Technician B says that when performing disc brake procedures, it is okay to let the calipers hang by the hoses. Who is correct?
   1. Technician A
   2. Technician B
   3. Both A and B
   4. Neither A nor B

5. Technician A says that rotors should be marked when removed from the hub so that it can be reinstalled in the same position. Technician B says that hub-style rotors may need a new grease seal installed before reinstalling the rotor. Who is correct?
   1. Technician A
   2. Technician B
   3. Both A and B
   4. Neither A nor B

6. Technician A says that excessive thickness variation typi­cally causes metal-to-metal contact. Technician B says that excessive lateral runout tends to cause the steering wheel to shimmy. Who is correct?
   1. Technician A
   2. Technician B
   3. Both A and B
   4. Neither A nor B

7. Technician A says that most manufacturers who allow ro­tors to be refinished prefer off-car machining in order to maximize runout tolerances. Technician B says that when a rotor is machined on the vehicle, it is refinished true to the hub. Who is correct?
   1. Technician A
   2. Technician B
   3. Both A and B
   4. Neither A nor B

8. Technician A says that hubless rotors can be centered with an adapter that drives the rotor from the center hole. Techni­cian B says that anti-chatter belts absorb vibration during the machining process to provide a smooth finish. Who is correct?
   1. Technician A
   2. Technician B
   3. Both A and B
   4. Neither A nor B

9. Technician A says that over-torqued lug nuts can cause wheel studs to break. Technician B says that the hub and flange must be replaced if wheel studs break on most vehicles. Who is correct?
   1. Technician A
   2. Technician B
   3. Both A and B
   4. Neither A nor B

10. Technician A says that pumping the brake pedal after brake work is important in order to adjust the caliper pistons and avoid a potential accident. Technician B says to be careful not to lose the bleeder screw dust caps because they must be rein­stalled. Who is correct?
    1. Technician A
    2. Technician B
    3. Both A and B
    4. Neither A nor B

Assignments

• Review all materials from this chapter and be prepared for a chapter quiz to be administered (date to be determined by instructor).
• Direct students to read the next chapter in Fundamentals of Automotive Maintenance and Light Repair, Second Edition as listed on your syllabus to prepare for the next class session.

Chapter 34

Disc Brake Systems Theory

Learning Objectives

After reading this chapter, you will be able to:

• 34-01 Describe disc brake fundamentals
• 34-02 Describe disc brake caliper operation
• 34-03 Describe the brake pad assembly
• 34-04 Describe brake rotor construction
• 34-05 Describe parking brakes on disc brakes

ASE Education Foundation Tasks

The following ASE Education Foundation Automobile Accreditation Tasks are covered in this chapter:

• VA4 Identify brake system components and configuration.

Readings and Preparation

• Review all instructional materials, including the chapter in Fundamentals of Automotive Maintenance and Light Repair, Second Edition, and all related presentation support materials.

Support Materials

• Lecture PowerPoint presentation, including all Skill Drills

Pre-Lecture

• You Are the Automotive Technician
  • A progressive case study that encourages critical thinking skills.
  • Direct students to read the “You Are the Automotive Technician” scenario found at the beginning of each chapter.
  • Group Activity: Direct students to review the discussion questions at the end of the scenario and prepare a response to each question. Facilitate a class discussion centered on the questions.
  • Homework Assignment: Ask students to turn in their comments on the questions.
• Teaching Tip: Explain to students how this material applies to the workplace. Provide an example of situation to make it relevant and meaningful. How does it fit into the broader picture? Is it building on something they already know? Will it help them master a skill? Students need to understand that what we are teaching is of importance on the job. This can be done by describing interesting disc brake system repairs you have experienced. You can also have students complete the online pre-test for this chapter in the CDX online system. This will help them understand what they do and do not know about disc brake systems.

Lecture

34-01 Describe disc brake fundamentals.

• The primary components of disc brakes are the rotors, the calipers, and the brake pads.
• The rotor is the rotating part of the brake system. Rotors are durable and can withstand the high temperatures and forces that occur during braking.
• Most rotors are made from cast iron, though in high-performance vehicles they may be made from composite materials such as ceramics and carbon fiber.
• The calipers straddle the rotors and house the brake pads and activating piston.
• They use hydraulic pressure from the master cylinder to apply the brake pads and are usually mounted to the steering knuckle or, in case of a non-steering axle, to a suspension component.
• The brake pads are located inside the caliper or caliper mounting bracket and are forced against the rotor to slow or stop the vehicle.
• A disc brake pad consists of friction material bonded or riveted to a steel backing plate. The friction material wears out over time and needs to be replaced periodically.
• When the brake pedal is depressed, the pushrod transfers the force to a hydraulic master cylinder via a brake booster.
• The hydraulic pressure from the master cylinder is transmitted via the brake lines to the pistons in the caliper, which operate on the friction pads to clamp the rotor and slow its rotation.
• The wheel hub may be part of the brake rotor, called a hub-style rotor, or the rotor may be bolted to the hub, called a hubless rotor.
• Disc brakes require much higher application force than drum brakes because they are not self-energizing. Manufacturers overcome this by equipping disc brake systems with brake boosters.
• The higher application force required makes using disc brakes as parking brakes difficult. Manufacturers may make the rear brake calipers more complicated or build an auxiliary drum-style parking brake into the center of the rear brake rotors, called a top-hat design.
• Disc brakes generate and transfer greater amounts of heat than drum brakes, as most of the friction area is exposed to air. This improves cooling and reduces the likelihood of brake fade.
• Disc brakes are also better at scraping water off the rotors, are self-adjusting, and are easier to service than drum brakes.
• However, disc brakes are more prone to making noise and warping, while thickness variations as small as 0.0003 inches can cause pedal pulsations.

34-02 Describe disc brake caliper operation.

• Disc brake calipers may be of two types: fixed calipers and sliding or floating calipers.
• All calipers are fitted with a bleeder screw at the top of the piston bore, which is used to remove air from within the system or while performing brake fluid changes.
• Fixed calipers are rigidly bolted in place and typically have one to four pistons on each side of the rotor. Hydraulic pressure rises equally on each side of the caliper, applying each brake pad equally.
• Floating or sliding calipers may have one or more piston located on only one side of the caliper, usually the inboard side of the rotor.
• The caliper is mounted on pins or slides, allowing the caliper to move from side to side as necessary.
• When the brakes are applied, the hydraulic pressure forces the piston and inboard brake pad toward the rotor. The caliper housing is then pushed away from the rotor, which pulls the outboard brake pad toward the rotor.
• Floating calipers are mounted by guide pins and bushings. As the calipers move on the pins, they should be lubricated with high-temperature, waterproof disc brake caliper grease.
• Sliding calipers have matching machined surfaces on the caliper and caliper mount. When serviced, the mounting surfaces should be cleaned and lubricated with the same caliper grease.
• The piston is sealed by a stationary square section sealing ring that is fitted in a machined groove in the caliper and pressed between the piston and caliper housing, called a square-cut O-ring.
• It keeps the high-pressure fluid from leaking and prevents air from being drawn into the system if the brake pedal is released too quickly.
• The outward movement of the piston deforms the O-ring slightly. When the brakes are released, the O-rings return to their original shape, retracting the piston and maintaining a small running clearance between the brake pad and the rotor.
• As the brakes wear, the piston has to move outward more than the sealing ring can flex. The piston slides through the ring in this situation and takes up the extra clearance, making the brakes self-adjusting.
• The outside of the sealing groove may be machined at an angle toward the rotor, which allows the O-ring to flex farther and hence retract the pistons farther when the brakes are released.
• These calipers are called low-drag calipers and use a quick take-up or fast-fill master cylinder to maintain adequate brake pedal reserve height.
• The primary sealing surface is the outside surface of the piston. It should be smooth and free from pitting or rust.
• Pistons may be chrome plated to give the surface a hard, wear- and corrosion-resistant surface.
• Pistons may also be made of phenolic resin, which is very dense once cooled and does not corrode or rust. These pistons also transfer heat more slowly than steel pistons, making them less likely to cause the brake fluid to boil.
• A dust boot seals the surfaces of the piston caliper and bore from outside dirt and moisture and is expandable to allow the piston to move outwards as the brake pads wear.

34-03 Describe the brake pad assembly.

• Disc brake pads consist of friction material bonded or riveted to a steel backing plate.
• Bonded linings are common on light duty vehicles because they are less expensive to build, although the bonding agent can fail under very high temperatures of heavy-duty use.
• Riveted linings are less susceptible to failure under high temperatures, but they pinch some of the lining material between the rivet head and the backing plate, and hence need to be changed sooner than bonded linings.
• The backing plate also often has lugs that correctly position the brake pads in the caliper assembly and help them maintain the proper position to the rotor.
• Materials that provide good braking at low pedal pressures tend to wear out sooner while materials that maintain stable friction coefficients over wider temperature ranges tend to require higher pedal pressures and put added wear in the brake rotor.
• Friction is the force that prevents two surfaces from sliding over each other. The amount of friction is expressed as a factor called the coefficient of friction.
• As heat in brake pads and linings builds up, the coefficient of friction reduces, also reducing stopping power. This is called brake fade.
• Friction materials used to be made of asbestos; however, this is hazardous, hence brake linings are now made from non-asbestos organic (NAO) materials, low-metallic NAO materials, semi-metallic materials, or ceramic materials.
• The choice of brake lining compound depends on stopping power, heat absorption and dispersion, resistance to fade, recovery from fade, wear rate, performance when wet, operating noise, and price.
• The Society of Automotive Engineers (SAE) has adopted letter codes to rate the coefficient of friction of brake lining materials, which is written on the edge of the linings and is called an edge code.
• The lower the letter, the less friction the material has and the harder the brake pedal has to be applied to achieve a given amount of stopping power.
• The lining is tested both cool and hot, with the rating being a two-letter designation: the first letter representing the cool performance and the second letter the hot performance.
• Brake squealing is caused by vibrations set up between the brake pad and rotor, and manufacturers have addressed this problem in a number of ways.
• Softer linings with higher coefficients of friction are less prone to noise than harder linings with a lower coefficient of friction.
• Brake pad shims and guides help cushion the brake pad and absorb some of the vibration.
• Springs that tightly hold the pads in place minimize vibration.
• Contouring and grooving the lining material minimizes vibration.
• Incorporating bendable tangs that can be crimped so that they are more firmly mounted in the caliper minimizes vibration.
• Noise reducing compounds can also be applied to the brake pads. Either a rubber compound is applied to the back of the pad, absorbing vibrations, or a liquid compound can be applied to the face of the lining, modifying the coefficient of friction slightly and making it less likely to squeal.
• Wear indicators warn the driver when the brake linings are worn to the minimum limit and help ensure that the brake linings do not wear down to the point where they do not perform their job anymore.
• Excessively thin brake linings heat up more quickly than thicker linings, which can lead to premature brake fade.
• A steel spring scratcher may be mounted to the brake pad with a part extending below the backing plate at the lining’s minimum wear thickness. When the friction material wears down far enough, the scratcher contacts the surface of the rotor and makes a squealing noise to indicate that service is needed.
• Some systems have an electric contact on the brake pad set at the pad’s minimum thickness.
• When the pad wears to this thickness, the contacts touch the rotor as the brakes are applied and complete a circuit that activates a warning light or message.

34-04 Describe brake rotor construction.

• The rotor must be strong and have a durable surface to withstand the high pressures applied by the brake pads. They should also be able to withstand the high temperatures generated due to friction.
• A composite rotor is a two-part rotor that uses a cast iron disc and a stamped steel center hat.
• Rotors may fail due to parallelism, also called thickness variation, which is any unevenness in the rotor surface. It causes the brake pedal to pulsate as thicker and thinner portions pass between the brake pads.
• Lateral runout or warpage is the side-to-side movement of the rotor surfaces as it turns. This tends to move the caliper pistons in the same direction as one another, causing the steering wheel to shimmy as the warped rotor follows the brake pads.
• Disc brakes use a dust shield to protect the rotor from dust, water, and other debris as well as to direct airflow to the rotor to assist with heat transfer to the atmosphere.
• Rotors may be solid or ventilated, with ventilated rotors using centrifugal force to move air through passageways between the friction surfaces from the center of the rotor.
• Disc brake rotors with holes or slots machined into their surface dissipate heat faster and help remove water quickly from between the pad and the rotor when driving in wet conditions.
• The pads wipe across the holes or slots as the brakes are applied, which prevents the surface of the lining from becoming glazed; however, this also reduces the overall life of the brake pad.

34-05 Describe parking brakes on disc brakes.

• Parking brakes should hold the vehicle for a given period of time on a specified grade in both directions. They must be activated separately from the service brakes, and the driver should be able to latch them in the applied position.
• Parking brakes on disc brake units are of two types: integrated parking brake caliper or the top-hat drum style.
• In an integrated caliper, a lever on the back of the caliper is pulled by a cable and turns a shaft that enters the rear of the caliper cylinder.
• The shaft has a coarse thread and is threaded to a nut assembly inside the piston. As the shaft is turned, it causes the piston to be forced outward, which applies the brakes.
• The top-hat design has a deeper offset than normal, which gives it the appearance of a top hat. The offset portion allows room for a drum surface within the center of the rotor.
• Drum brake shoes are forced outwards mechanically to contact the inside of the brake drum, which locks the wheel.
• The electric parking brake uses an electric motor to apply the disc brake assemblies. This may be cable-style, which pulls standard parking brake cables or uses an electric motor mounted to the caliper, which directly applies the brake pads.
• Electric parking brakes can also be integrated with the CAN bus system to provide additional features such as hill assist, which automatically holds the vehicle when it is stopped on a hill, or it may also work with the vehicle’s proximity sensor to stop the vehicle from striking an object when maneuvering.

Post-Lecture

This section contains various student-centered end-of-chapter activities designed as enhancements to the instructor’s presentation. As time permits, these activities may be presented in class. They are also designed to be used as homework activities.

1. Direct students to read and individually answer the question sets located in the Wrap-Up section at the end of each chapter. Allow approximately 10–20 minutes for this part of the activity.
2. Facilitate a class review and discussion of the answers, allowing students to correct responses as may be needed. Use the answers noted in the Answer Key to assist in building this review.
3. You may wish to ask students to complete this activity on their own and turn in their answers on a separate piece of paper.

Review Questions

This question set is designed to assist students in understanding the chapter content by asking knowledge-based comprehension questions.

1. Which of the following is a component in the disc brake system?
   1. Brake rotor
   2. Brake drum
   3. Self adjuster
   4. Wheel cylinder

2. How often are disc brakes adjusted by a technician?
   1. Once per year
   2. At every oil change
   3. Every 30,000 miles
   4. Never

3. All of the following are types of a disc brake caliper EXCEPT:
   4. low drag.

4. How is a brake caliper piston sealed?
   1. A square cut O-ring
   2. A paper gasket
   3. A liquid RTV
   4. A brass ring

5. Some disc brake pads have their linings glued or bonded to them. Others are:
   4. press fit.

6. Which of the following is something that engineers consider when they design brake pads for a vehicle?
   1. Wheel cylinder size
   2. Piston pushback pressure
   3. Resistance to fade
   4. Recovery from boil

7. Why would a manufacturer use carbon ceramic brake rotors rather than cast iron brake rotors?
   1. Because it is less expensive to manufacture
   2. Because it is better for the environment
   3. Because it is lighter and withstands heat better
   4. Because it never wears out

8. What component is responsible for directing air toward the rotor and protecting from road debris?
   1. The dust shield
   2. The cooling fan
   3. The rotor hub
   4. The rotor slots

9. A vehicle equipped with rear disc brakes and a pedal-actuated rear parking brake is likely to be operated by a cable and:
   3. spoke lock.
   4. parking pawl.

10. What are parking brakes that use brake shoes inside of the rotor often called?
    1. Mini drum
    2. Lock-in barrel
    3. Top hat
    4. Combo shoes

ASE Technician A/Technician B Style Questions

This question set is designed to assist students in gaining a further understanding of and familiarity with ASE Technician A/Technician B questions.

1. A brake system is being discussed. Technician A states that disc brakes require more clamping pressure than drum brakes. Technician B states that disc brakes can transfer heat faster than drum brakes. Who is correct?
   1. Technician A
   2. Technician B
   3. Both A and B
   4. Neither A nor B

2. A disc brake system being discussed. Technician A states that calipers straddle the rotor and house the brake pads. Technician B states that brake calipers expand the brake pads into the center of the rotor. Who is correct?
   1. Technician A
   2. Technician B
   3. Both A and B
   4. Neither A nor B

3. Disc brake calipers are being discussed. Technician A states that the caliper bleeder is normally mounted at the bottom of the caliper. Technician B states that floating calipers are more precise than fixed since they are firmly bolted in place. Who is correct?
   1. Technician A
   2. Technician B
   3. Both A and B
   4. Neither A nor B

4. A brake caliper is being discussed. Technician A states that floating caliper guide pins and bushings must be lubricated with high-temperature grease when serviced. Technician B states that the caliper piston O-ring retracts the piston. Who is correct?
   1. Technician A
   2. Technician B
   3. Both A and B
   4. Neither A nor B

5. Brake pads are being discussed. Technician A states that brake pads should have the lowest coefficient of friction possible. Technician B states that brake pads are currently made of asbestos. Who is correct?
   1. Technician A
   2. Technician B
   3. Both A and B
   4. Neither A nor B

6. A brake warning lamp is being discussed. Technician A states that the light is most likely caused by low brake fluid or a parking brake left on. Technician B states that some manufacturers have electrical contacts installed on the brake pad that will turn on this light when the brake pads are worn too low. Who is correct?
   1. Technician A
   2. Technician B
   3. Both A and B
   4. Neither A nor B

7. Brake rotors are being discussed. Technician A states that brake rotors that are constructed of two materials are known as composite rotors. Technician B states that cast iron is commonly used in brake rotors because it is strong, and withstands heat well. Who is correct?
   1. Technician A
   2. Technician B
   3. Both A and B
   4. Neither A nor B

8. A high-performance vehicle comes in to the shop. Technician A states that it is likely to have standard solid brake rotors. Technician B states that the rotors may have holes or slots for heat dissipation. Who is correct?
   1. Technician A
   2. Technician B
   3. Both A and B
   4. Neither A nor B

9. A vehicle with disc brakes being discussed. Technician A states that the brake rotors often have a minimum thickness stamped on the rotor. Technician B states that if the brake rotors are too thick, they will not be able to withstand high levels of heat and could warp. Who is correct?
   1. Technician A
   2. Technician B
   3. Both A and B
   4. Neither A nor B

10. A vehicle with an electronic parking brake is being discussed. Technician A states that the electronic parking brake may use an electric motor that pulls on the parking brake cables. Technician B states that the electronic parking brake may be integrated with the CAN bus system which could allow it to be used by other systems. Who is correct?
    1. Technician A
    2. Technician B
    3. Both A and B
    4. Neither A nor B

Assignments

• Review all materials from this chapter and be prepared for a chapter quiz to be administered (date to be determined by instructor).
• Direct students to read the next chapter in Fundamentals of Automotive Maintenance and Light Repair, Second Edition as listed on your syllabus to prepare for the next class session.

Chapter 33

Servicing Hydraulic Systems and Power Brakes

Learning Objectives

After reading this chapter, you will be able to:

• 33-01 Describe brake repair liability and brake tools.
• 33-02 Inspect and test brake fluid.
• 33-03 Bleed and flush brake systems.
• 33-04 Measure brake pedal height, free play, and travel.
• 33-05 Describe general brake hydraulic system diagnosis.
• 33-06 Perform master cylinder service.
• 33-07 Test vacuum-style brake boosters.
• 33-08 Service brake lines and hoses.
• 33-09 Test the operation of the brake warning lamp and stop lights.

ASE Education Foundation Tasks

The following ASE Education Foundation Automobile Accreditation Tasks are covered in this chapter:

• VB1 Describe proper brake pedal height, travel, and feel.
• VB2 Check master cylinder for external leaks and proper operation.
• VB3 Inspect brake lines, flexible hoses, and fittings for leaks, dents, kinks, rust, cracks, bulging, wear, and loose fittings/supports.
• VB4 Select, handle, store, and fill brake fluids to proper level; use proper fluid type per manufacturer specification.
• VB5 Identify components of hydraulic brake warning light system.
• VB6 Bleed and/or flush brake system.
• VB7 Test brake fluid for contamination.
• VE1 Check brake pedal travel with, and without, engine running to verify proper power booster operation.
• VE2 Identify components of the brake power assist system (vacuum and hydraulic); check vacuum supply (manifold or auxiliary pump) to vacuum-type power booster.
• VF3 Check parking brake operation and parking brake indicator light system operation; determine necessary action.
• VF4 Check operation of brake stop light system.

Readings and Preparation

• Review all instructional materials, including the chapter in Fundamentals of Automotive Maintenance and Light Repair, Second Edition, and all related presentation support materials.

Support Materials

• Lecture PowerPoint presentation, including all Skill Drills

Pre-Lecture

• You Are the Automotive Technician
  • A progressive case study that encourages critical thinking skills.
  • Direct students to read the “You Are the Automotive Technician” scenario found at the beginning of each chapter.
  • Group Activity: Direct students to review the discussion questions at the end of the scenario and prepare a response to each question. Facilitate a class discussion centered on the questions.
  • Homework Assignment: Ask students to turn in their comments on the questions.
• Teaching Tip: Explain to students how this material applies to the workplace. Provide an example of a situation to make it relevant and meaningful. How does it fit into the broader picture? Is it building on something they already know? Will it help them master a skill? Students need to understand that what we are teaching is of importance on the job. This can be done by describing the results of faulty repairs on the brake’s hydraulic system. You can also have students complete the online pre-test for this chapter in the CDX online system. This will help them understand what they do and do not know about the maintaining the brake’s hydraulic system.

Lecture

33-01 Describe brake repair liability and brake tools.

• While improperly repaired brakes can function reasonably well under normal driving situations, they can fail during a panic situation, increasing likelihood of accidents, injury, or death.
• Shops and technicians risk being found criminally negligent for improper brake repairs or failure to properly tighten components, so always follow the manufacturer’s procedures when servicing brake systems and create processes to ensure that steps of a job are not forgotten.
• Common hydraulic system maintenance tools are:
  • Brake bleeder wrenches that are used to open and close bleeder screws
  • Flare nut wrenches to loosen and tighten brake line fittings
  • Vacuum brake bleeders to pull brake fluid from the hydraulic braking system

33-02 Inspect and test brake fluid.

• Brake fluid is a non-top-off fluid, and there are only two reasons that cause the brake fluid level to go down: if the hydraulic system has a leak or worn disc brake linings.
• Brake fluid levels should be inspected during every oil change.
• Brake fluid flushing and replacement is a maintenance item based on either manufacturer time specifications or on the condition.
• To determine if the brake fluid should be flushed, check time/mileage in manufacturer specifications, use a digital multimeter (DMM)-galvanic reaction test to test the level of moisture, boiling point test to measure the boiling point, or use a test strip that measures specific chemicals/metals in the brake fluid to indicate whether there is a chemical breakdown of the brake fluid.

33-03 Bleed and flush brake systems.

• Bleeding the brakes is the process of removing any air from the system, because if air enters the brake system, brake pressure does not build up fully.
• Different brake bleeding methods include manual bleeding, vacuum bleeding, and pressure bleeding, all of which usually follow the sequence of right rear wheel (RR), left rear wheel (LR), right front wheel (RF), and left front wheel.
• Some concerns during the bleeding process are as follows:
  • Do not bleed one wheel so much that the reservoir runs dry, since air will enter.
  • Never push the brake pedal past its normal operating travel, to prevent damage to the master cylinder.
  • When using a vacuum bleeder, if the fluid coming out is clear, all air should be out of the system.
  • During the vacuum bleeding process, watch the reservoir carefully to top it off and avoid getting air in the system.
• Flushing brake fluid uses the same process as brake bleeding, and is designed not only to remove trapped air, but also to replace all the old brake fluid with new brake fluid.

33-04 Measure brake pedal height, free play, and travel.

• The proper brake pedal height helps to ensure that the brake pedal has enough starting height to fully apply the brakes.
• Free play is the amount of clearance between the joints in the brake pedal linkage.
• Brake pedal travel is the distance the brake pedal travels from its rest position to its applied height.
• Pedal height can be obstructed if floor mats prevent full travel of the pedal, or if the brake linkage or supports are bent, or bushings are worn.
• If the free play is out of specifications, it may be caused by a misadjusted brake pedal pushrod, worn brake pedal bushings, or bent linkage.
• If the reserve height or pedal travel measurement is out of specifications, it could be caused by a misadjusted brake pedal pushrod, or a hydraulic brake system fault.

33-05 Describe general brake hydraulic system diagnosis.

• Hydraulic braking system diagnosis follows the strategy-based diagnostic process where information is obtained from the customer, from the test drive, and by researching the manufacturer’s TSBs or diagnostic processes.
• This is used to develop a focused testing plan that involves performing tests in the shop with a scan tool, pressure gauges, or a DMM, and may also require disassembly and visual inspection or measurements of the suspected component or system.
• Once a cause of the fault is identified and repair is complete, it must be verified that the repair corrected the customer concern by retesting the component or system with the test that identified the fault.

33-06 Perform master cylinder service.

• The master cylinder is inspected for internal and external leaks if the brake pedal sinks when the brakes are applied, the brake fluid is low in the reservoir, the brake warning light is on, or the brake pedal reserve height is too low.
• Leaks can be found by inspecting for brake fluid on the inside of the vacuum hose to the power booster, as well as checking brake line fittings, sensor connections, reservoir seals, and the areas at the rear of the master cylinder near the power booster.
• If the pedal sinks and there is no external leak in the brake system, there is likely an internal leak in the master cylinder that can be found by the visual method or the block-off method.
• Bench bleeding the master cylinder is required when the master cylinder is being replaced because removing all the air from the master cylinder allows it to build normal pressure when bleeding the system.
• If master cylinder pushrod length is too short, the brake pedal needs to be depressed further than specified and if it is too long, it could prevent the master cylinder piston from returning far enough.

33-07 Test vacuum-style brake boosters.

• When the vehicle has an unlocated vacuum leak, vacuum boosters should be tested by performing the following: brake pedal free travel test, performance/operation test and external and internal leak tests on single-and dual-diaphragm boosters.
• Power booster testing starts with a brake pedal free travel test. Although insufficient free travel can cause the brakes to drag due to trapped fluid pressure, excessive free travel reduces the amount of reserve pedal for braking in the event of a hydraulic brake system leak.
• The brake booster must have an adequate amount of vacuum to operate correctly since insufficient vacuum causes the driver to increase foot pressure to activate the brakes.
• Check the power booster unit for external leaks from points such as the vacuum check. valve and/or grommet, the front or rear seals of the unit, the atmospheric valve at the rear of the booster, or the case where the halves are crimped together, and if a hole has worn or rusted through the case.
• A check valve operation test is performed to ensure air should flow from the booster side of the check valve to the engine side only.

33-08 Service brake lines and hoses.

• Brake lines and brake hoses should be inspected for corrosion from chemicals, dents, kinks, cuts, cracking, bulging, and abrasion.
• Before replacement, brake lines should be disconnected from fittings with the double-wrench method.
• To fabricate brake lines, the inverted double flare or ISO flare methods are used.

33-09 Test the operation of the brake warning lamp and stop lights.

• A mechanical brake warning lamp system includes a lightbulb in series, with as many as four switches connected in parallel.
• When diagnosing the brake warning lamp, ensure the bulb is operational, check the fuse with a test light, test whether any of the switches need to be adjusted or replaced, or if there is a short in the wiring.
• In a CAN bus circuit, the parking brake sensor and the low brake fluid sensors send status signals over the CAN bus network, so diagnosis is done either by a scan tool capable of checking the system or a DMM used to perform specific tests.
• The mechanical stop light system consists of a normally closed switch in series with two to six brake lightbulbs connected in parallel with each other and protected by a fuse.
• While diagnosing a problem with the stop light system, observe the wiring diagram, and check components such as fuse, stop light switch, and stop light ground circuit before using a DMM to observe if bulbs, terminals, or wires have burnt out.

Post-Lecture

This section contains various student-centered end-of-chapter activities designed as enhancements to the instructor’s presentation. As time permits, these activities may be presented in class. They are also designed to be used as homework activities.

1. Direct students to read and individually answer the question sets located in the Wrap-Up section at the end of each chapter. Allow approximately 10–20 minutes for this part of the activity.
2. Facilitate a class review and discussion of the answers, allowing students to correct responses as may be needed. Use the answers noted in the Answer Key to assist in building this review.
3. You may wish to ask students to complete this activity on their own and turn in their answers on a separate piece of paper.

Review Questions

This question set is designed to assist students in understanding the chapter content by asking knowledge-based comprehension questions.

1. Brake lining material dust may be hazardous to breathe because it could contain:
   1. carbon dioxide.
   2. carbon monoxide.
   3. gasoline vapors.

2. When testing brake fluid, any voltage reading less than __________ is commonly acceptable.
   1. 3 volts AC
   2. 0 volts AC
   3. 3 volts DC
   4. 0 volts DC

3. Which method of brake fluid bleeding is ideal for when the fluid needs to be flushed out of a brake system?
   1. Manual bleeding
   2. Vacuum bleeding
   3. Pressure bleeding
   4. Free play bleeding

4. What could happen if the brake pedal is pushed past its normal travel during manual brake bleeding?
   1. The parking brake lever may stick.
   2. The firewall may flex making it hard to bleed.
   3. The master cylinder fluid lines may twist or kink.
   4. The master cylinder piston seals may leak.

5. If the pedal height is incorrect on a nonadjustable pedal assembly, what could be the cause?
   1. Leaking master cylinder cup seals
   2. Misadjusted drum brake shoes
   3. Air in the hydraulic system
   4. Worn pedal bushings

6. Some hydraulic brake concerns can be hard to identify. What should be done if you can’t verify the problem?
   1. Tell the customer there is nothing wrong and give the vehicle back.
   2. Search the Internet for a concern that sounds similar and diagnose that.
   3. Replace each of the parts that might cause the customer concern.
   4. Test drive the vehicle with the customer to gain a clear understanding of the concern.

7. What does a master cylinder pushrod that is adjusted too long likely cause?
   1. Low brake pedal during brake application
   2. A spongy brake pedal feel
   3. Trapped pressure that applies the brakes when the pedal is released
   4. Stripped brake line fittings

8. A vacuum booster that leaks vacuum may cause all of the following, EXCEPT:
   1. A lean running engine
   2. Incorrect push rod adjustment
   3. A rough idling engine
   4. Immediate loss of power brakes when the engine stalls

9. Why should the brake pedal be held in the depressed position when replacing brake lines or hoses?
   1. To prevent brake fluid drainage
   2. To prevent master cylinder return spring damage
   3. To keep the brake lights from discharging the battery
   4. To pressurize the new lines as soon as they are installed

10. Which service information document shows the path of electrical current flow and components involved in the stop light system?
    1. Parts and labor guide
    2. Removal and installation of the tail lamp assembly
    3. Stop lamp wiring diagram
    4. Stop lamp connector pin chart

ASE Technician A/Technician B Style Questions

This question set is designed to assist students in gaining a further understanding of and familiarity with ASE Technician A/Technician B questions.

1. Technician A says that technicians are not held legally responsible for improper brake repairs. Technician B says that it is important to develop work routines that eliminate the potential for errors. Who is correct?
   1. Technician A
   2. Technician B
   3. Both A and B
   4. Neither A nor B

2. Technician A says that brake fluid condition can be tested with a digital multimeter. Technician B says that brake fluid should be topped off whenever it is low. Who is correct?
   1. Technician A
   2. Technician B
   3. Both A and B
   4. Neither A nor B

3. Technician A says that manual bleeding of a brake hydraulic system typically requires the help of an assistant. Technician B says that the order in which the brakes are bled is not important. Who is correct?
   1. Technician A
   2. Technician B
   3. Both A and B
   4. Neither A nor B

4. Technician A says that free play is measured by subtracting applied brake pedal height from the brake pedal height measurement at rest. Technician B says that if free play is out of specifications, it is likely a pushrod out of adjustment. Who is correct?
   1. Technician A
   2. Technician B
   3. Both A and B
   4. Neither A nor B

5. While discussing brake hydraulic system diagnosis, Technician A says that technical service bulletins (TSBs) should typically be researched before symptom diagnosis testing. Technician B says that once a fault is found, there may be an underlying root cause that requires further investigation. Who is correct?
   1. Technician A
   2. Technician B
   3. Both A and B
   4. Neither A nor B

6. Technician A says that with the engine running and the brakes applied, the brake pedal should hold its position. Technician B says that bench bleeding a master cylinder no longer saves time during replacement and is unnecessary. Who is correct?
   1. Technician A
   2. Technician B
   3. Both A and B
   4. Neither A nor B

7. Technician A says that while testing a vacuum booster, the pedal should not drop when the engine is started. Technician B says that the pressure supplied to the vacuum booster should be about 10 in/Hg lower than engine manifold vacuum. Who is correct?
   1. Technician A
   2. Technician B
   3. Both A and B
   4. Neither A nor B

8. Technician A says that brake lines should be checked for abrasion and rust. Technician B says that open-end wrenches are just as good as flare nut wrenches when removing brake line fittings. Who is correct?
   1. Technician A
   2. Technician B
   3. Both A and B
   4. Neither A nor B

9. Technician A says that a brake fluid leak may cause the red brake warning light to illuminate. Technician B says that low brake fluid in the master cylinder reservoir may cause the red brake warning light to illuminate. Who is correct?
   1. Technician A
   2. Technician B
   3. Both A and B
   4. Neither A nor B

10. Technician A says that the normal stop lamps may be powered separately from the center high-mount stop lamp (CHMSL). Technician B says that a defective fluid level switch may cause the center high-mount stop lamp (CHMSL) to be inoperative. Who is correct?
    1. Technician A
    2. Technician B
    3. Both A and B
    4. Neither A nor B

Assignments

• Review all materials from this chapter and be prepared for a chapter quiz to be administered (date to be determined by instructor).
• Direct students to read the next chapter in Fundamentals of Automotive Maintenance and Light Repair, Second Edition as listed on your syllabus to prepare for the next class session.

Chapter 32

Hydraulics and Power Brakes Theory

Learning Objectives

After reading this chapter, you will be able to:

• 32-01 Describe hydraulic principles.
• 32-02 Describe brake fluid types and characteristics.
• 32-03 Describe master cylinder construction and operation.
• 32-04 Describe quick take-up and ABS master cylinders.
• 32-05 Describe brake pedal assemblies and divided hydraulic systems.
• 32-06 Describe brake lines and
• 32-07 Describe proportioning valves and their operation.
• 32-08 Describe metering, pressure differential, and combination valves.
• 32-09 Describe brake warning light and stop light operation.
• 32-10 Describe the operation of vacuum brake boosters.
• 32-11 Describe the operation of hydraulic brake boosters.

ASE Education Foundation Tasks

The following ASE Education Foundation Automobile Accreditation Tasks are covered in this chapter:

• VA4 Identify brake system components and configuration.
• VE2 Identify components of the brake power assist system (vacuum and hydraulic); check vacuum supply (manifold or auxiliary pump) to vacuum-type power booster.

Readings and Preparation

• Review all instructional materials, including the chapter in Fundamentals of Automotive Maintenance and Light Repair, Second Edition, and all related presentation support materials.

Support Materials

• Lecture PowerPoint presentation, including all Skill Drills

Pre-Lecture

• You Are the Automotive Technician
  • A progressive case study that encourages critical thinking skills.
  • Direct students to read the “You Are the Automotive Technician” scenario found at the beginning of each chapter.
  • Group Activity: Direct students to review the discussion questions at the end of the scenario and prepare a response to each question. Facilitate a class discussion centered on the questions.
  • Homework Assignment: Ask students to turn in their comments on the questions.
• Teaching Tip: Explain to students how this material applies to the workplace. Provide an example of a situation to make it relevant and meaningful. How does it fit into the broader picture? Is it building on something they already know? Will it help them master a skill? Students need to understand that what we are teaching is of importance on the job. This can be done by describing interesting hydraulic brake system repairs you have experienced. You can also have students complete the online pre-test for this chapter in the CDX online system. This will help them understand what they do and do not know about the brake’s hydraulic system.

Lecture

32-01 Describe hydraulic principles.

• Pascal’s law states that pressure applied to a fluid in one part of a closed system will be transmitted without loss to all other areas of the system.

• Pressure created in the master cylinder is transmitted equally through the hydraulic braking system.
• Varying amounts of mechanical force can be extracted from a single amount of hydraulic fluid pressure.
• Input force is the force applied to the input piston is measured in pounds (lb), newtons (N), or kilograms (kg).
• The working pressure of the hydraulic fluid is expressed as the amount of force per specified area.
• Output force is exerted by the output piston and is expressed as pounds, newtons, or kilograms.

32-02 Describe brake fluid types and characteristics.

• Brake fluid is hydraulic fluid that has specific properties designed for mobile applications; it is used to transfer force, while under pressure, through hydraulic lines to the wheel braking units.
• Standard brake fluid is harmful to painted surfaces and is hygroscopic.
• Brake fluids are graded against compliance standards set by the U.S. Department of Transportation (DOT).
• Brake fluids are tested to ensure they meet the standards for pH value, viscosity, resistance to oxidation, stability, and boiling point.

32-03 Describe master cylinder construction and operation.

• The master cylinder converts the brake pedal force into hydraulic pressure, which is then used to operate the wheel brake units.
• The master cylinder piston is operated by a pushrod from the power booster or the brake pedal.
• Single-piston master cylinders have one piston with two cups: a primary cup and a secondary cup. The primary cup seals the pressure in the cylinder; the secondary cup prevents loss of fluid past the rear end of the piston.
• An outlet port links the cylinder to the brake lines, an inlet port connects the reservoir with the space around the piston and between the piston cups, and a compensating port connects the reservoir to the cylinder, just barely ahead of the primary cup.
• The process of brake fluid moving past the primary seal on the return stroke is called recuperation.
• On a drum brake system, brake fluid pressure is held slightly above atmospheric pressure through a residual pressure valve.
• Tandem master cylinders combine two master cylinders within a common housing, which share a common cylinder bore.
• A tandem cylinder has a primary piston and a secondary piston. The primary piston is in the rear of the cylinder and is pushed directly by the pushrod; the secondary piston is in the front of the cylinder.
• Just like the single-piston master cylinder, the tandem master cylinder can develop a low-pressure area.
• If the secondary circuit fails, the primary system pushes the secondary piston until it makes contact with the end of the cylinder bore.
• If the primary circuit fails, no pressure is generated to move the secondary piston.
• A differential pressure switch in the master cylinder or hydraulic system is activated if there is a leak in the system, which turns on the brake warning light.
• Master cylinder reservoirs can be built into the master cylinder housing and formed on top of the master cylinder, using the same material.
• On two-piece master cylinders, the reservoirs are usually made of a see-through plastic material; grommets or O-rings are used to seal them to the master cylinder.
• Most modern master cylinder reservoirs are equipped with a low brake fluid level float switch.

32-04 Describe quick take-up and ABS master cylinders.

• Quick take-up master cylinders are used on disc brake systems that are equipped with low-drag brake calipers.
• Quick take-up master cylinders use a relatively large-diameter piston in the rear of the cylinder.
• Once the pressure rises above a predetermined point, a quick take-up valve opens, and the standard pistons take over.
• The ABS master cylinder is a tandem master cylinder used in divided systems.
• The primary chamber still uses a compensating port and an inlet port; the secondary piston incorporates a center valve.

32-05 Describe brake pedal assemblies and divided hydraulic systems.

• The brake pedal uses leverage to multiply the effort from the driver’s foot to the master cylinder.
• Different lever designs can be engineered to alter the brake pedal effort required of the driver.
• Brake pedals are covered with a rubber nonslip cover to maintain sure footing.
• The brake pedal is usually suspended from a bracket between the dash panel and the firewall.
• Brake pedals must be free to return to their starting position when pressure is removed.
• The spring action also causes the brake pedal to push the brake light switch open.
• The type of vehicle is a major factor in determining how its hydraulic system should be divided.
• In a front-engine, rear-wheel car, the braking system is divided in a vertical, or front–rear, split.
• Front-engine, front-wheel-drive vehicles use a braking system split in a diagonal, or X, pattern.
• An alternative arrangement for front-engine, front-wheel drive vehicles is an L-split.

32-06 Describe brake lines and hoses

• Brake lines and hoses carry brake fluid from the master cylinder to the brake units and are similar on all brake systems and passenger vehicles.
• They are attached to the body with clips or brackets to minimize damage; in some vehicles, the brake lines are located inside the vehicle.
• The brake lines must be able to transmit considerable hydraulic pressure and are made of seamless, double-walled steel.

• If a brake line is damaged, it is common practice to replace the entire brake line with a factory replacement rather than repair it.
• The inverted double flare is created by first flaring the end of the tube outward in a Y shape, then folding it back on itself.
• The International Standards Organization (ISO) flare is sometimes called a “bubble flare”.
• A flexible section of the brake lines must be included between the body and suspension.
• The flexible brake hoses transmit the brake system hydraulic pressures to the wheel units.
• Brake hoses are made of several layers of alternating materials. The inside of the hose has a liner that helps seal the brake fluid in and keep out any moisture. The liner is wrapped with two or more layers of flexible webbing. These layers are covered with a tough, flexible outer housing jacket designed to resist abrasion and damage.
• Brake hoses should be inspected periodically for damage or defects, which include cracks, bulges, abrasion or wear, kinks, and internal deterioration causing blockage of the passageway.
• Many brake hoses use banjo fittings to connect the hose to the wheel unit. A banjo fitting comprises a banjo bolt and two copper or aluminum sealing washers.

32-07 Describe proportioning valves and their operation.

• The hydraulic braking system must be controlled accurately to maintain adequate control of the vehicle during braking.
• The following components are used to modify or monitor the brake pressure:
• Proportioning valves
• Metering valves
• Pressure differential valves
• Antilock hydraulic control units
• Proportioning valves reduce brake pressure to the rear wheels under certain circumstances and can be pressure sensitive or load sensitive.
• The pressure-sensitive proportioning valve adjusts the braking force under heavy braking pressure.
• The poppet valve holds against its retainer by a light return spring.
• Aftermarket adjustable proportioning valves are available for performance applications; they have a method of adjusting the crack point of the proportioning valve.
• The load-sensitive proportioning valve modifies brake pressure according to vehicle load.
• Many ABS-equipped vehicles integrate an electronic brake proportioning function in the system, which uses the hydraulic control unit to control pressure to the rear brake unit.

32-08 Describe metering, pressure differential, and combination valves.

• Metering valves are used on vehicles with a disc/drum brake combination to hold off the initial application of the front brakes.
• The metering valve operates like a radiator cap and has a spring that holds the metering valve closed until a specified pressure is reached.
• A pressure differential valve monitors any pressure difference between the two separate brake circuits.
• The combination valve combines the hydraulic brake system valves into one unit; they can include the pressure differential valve, metering valve, and proportioning valve.

32-09 Describe brake warning light and stop light operation.

• The brake warning light is located on the instrument panel and is designed to warn the driver of a condition in the brake system that needs attention.
• Stop lights are also called brake lights and are designed to warn others that the vehicle is braking.

32-10 Describe the operation of vacuum brake boosters.

• A power brake booster assists the driver in applying the brakes.
• They use an external source of force to multiply the driver’s pedal effort to increase the force applied to the master cylinder pistons.
• There are two main types of power brake units: vacuum-assist and hydraulic-assist.
• The most common types of vacuum boosters are the single diaphragm and the dual diaphragm.
• When the driver steps on the brake pedal, it moves the brake pedal pushrod forward. The pushrod transmits movement through the power unit to the master cylinder, the master cylinder pistons apply the brakes, a hose connects the intake manifold to a vacuum check valve on the power brake unit, and the booster chambers are separated by a flexible rubber diaphragm attached to the diaphragm plate.
• Dual-diaphragm power boosters are smaller in diameter to better fit in the limited space under the hood of some vehicles; however, two smaller diaphragms in tandem are used, one behind the other.

32-11 Describe the operation of hydraulic brake boosters.

• The hydraulic booster system uses hydraulic pressure generated by the power steering pump and is particularly suitable to vehicles with diesel engines.
• The hydraulic booster uses pressure from the power steering fluid that is circulating through the system.
• Accumulators assist in maintaining a reserve of system pressure.
• Electrohydraulic braking (EHB) uses an electrically-driven hydraulic pump.

Post-Lecture

This section contains various student-centered end-of-chapter activities designed as enhancements to the instructor’s presentation. As time permits, these activities may be presented in class. They are also designed to be used as homework activities.

1. Direct students to read and individually answer the question sets located in the Wrap-Up section at the end of each chapter. Allow approximately 10–20 minutes for this part of the activity.
2. Facilitate a class review and discussion of the answers, allowing students to correct responses as may be needed. Use the answers noted in the Answer Key to assist in building this review.
3. You may wish to ask students to complete this activity on their own and turn in their answers on a separate piece of paper.

Review Questions

This question set is designed to assist students in understanding the chapter content by asking knowledge-based comprehension questions.

1. Pascal’s law is behind the hydraulic principles that is applied to brakes. What is Pascal’s law?
   1. Fluid with pressure in part of a closed system will transmit higher pressure to other parts of the system.
   2. Fluid with pressure in a closed system will transmit with no loss to other parts of the system.
   3. Fluid with pressure in a closed system will transmit with some loss to other parts of the system.
   4. Fluid with pressure in part of a closed system will transmit with some loss to other parts of the system.

2. Which of the brake fluid types are silicone based?
   1. Dot 3
   2. Dot 5
   3. Dot 5.1
   4. Dot 4

3. The master cylinder uses hydraulic pressure to operate which units?
   1. Wheel brake
   2. Steering wheel
   3. Front wheels
   4. Input piston

4. Quick take-up master cylinders are used on what systems?
   1. Disc brake systems with ABS
   2. Disc brake systems with low drag calipers
   3. Disc/drum split systems
   4. Front/rear divided systems

5. What is the major factor(s) that determine(s) how a brake system is divided front to rear?
   1. Weight of the vehicle with passengers
   2. Year of the vehicle
   3. Height of the vehicle
   4. Weight distribution of the vehicle

6. What is the purpose of brake lines and hoses?
   1. To carry brake fluid from the master cylinder to the brake units
   2. To carry brake fluid from the power brake booster to the master cylinder
   3. To modify the brake fluid pressure to the brake units
   4. To protect the brake units from corrosion

7. How do pressure-sensitive proportioning valves affect the rear brakes?
   1. Increase brake pressure under light braking
   2. Increase brake pressure under heavy braking
   3. Decrease brake pressure under light braking
   4. Decrease brake pressure under heavy braking

8. What does the metering valve do?
   1. Delays the first application of the front brakes
   2. Monitors pressure differences between both brake circuits
   3. Limits the pressure to the rear brake units
   4. Centers the pressure differential valve

9. What is the purpose of the brake warning light?
   1. To notify the driver of high brake fluid level
   2. To notify the driver the brake system needs attention
   3. To notify others the vehicle is braking
   4. To notify the driver the vehicle is braking

10. How does the power brake assist the driver?
    1. It uses an outside source of force to increase the driver’s pedal effort.
    2. It recycles the brake fluid to increase the driver’s pedal effort.
    3. It uses a long lever to increase the driver’s pedal effort.
    4. It uses the pushrod length to increase the driver’s pedal effort.

ASE Technician A/Technician B Style Questions

This question set is designed to assist students in gaining a further understanding of and familiarity with ASE Technician A/Technician B questions.

1. A brake system is being discussed. Technician A states that a soft or spongy pedal is a good indication that there could be air in the hydraulic system. Technician B states that engineers use different input and output piston sizes to precisely control brake unit output force. Who is correct?
   1. Technician A
   2. Technician B
   3. Both A and B
   4. Neither A nor B

2. A hydraulic brake system is being discussed. Technician A states that brake fluid must have a high boiling point since brakes create a lot of heat. Technician B states that hygroscopic means that brake fluid will not absorb water. Who is correct?
   1. Technician A
   2. Technician B
   3. Both A and B
   4. Neither A nor B

3. A hydraulic brake system is being discussed. Technician A states that the brake master cylinder functions as an output piston. Technician B states that the single master cylinder has replaced the tandem master cylinder for increased safety. Who is correct?
   1. Technician A
   2. Technician B
   3. Both A and B
   4. Neither A nor B

4. A vehicle comes in the shop with brake-related complaints. Technician A states that the brake system is normally split 50% front and 50% rear on front-wheel-drive vehicles. Technician B states that malfunctioning brake lights can be caused by a misadjusted brake light switch at the brake pedal. Who is correct?
   1. Technician A
   2. Technician B
   3. Both A and B
   4. Neither A nor B

5. A hydraulic brake system is being discussed. Technician A states that a leaking brake line could be repaired with a new section of copper tubing. Technician B states that when fabricating a new brake line, a tubing bender should be used. Who is correct?
   1. Technician A
   2. Technician B
   3. Both A and B
   4. Neither A nor B

6. A vehicle with a brake problem is being discussed; the rear wheels locks up when braking. Technician A states that the pressure-sensitive proportioning valve could be malfunctioning. Technician B states that the load-sensitive proportioning valve could require adjustment. Who is correct?
   1. Technician A
   2. Technician B
   3. Both A and B
   4. Neither A nor B

7. A metering valve is being discussed. Technician A states that a defective metering valve could cause the rear brakes to apply too quickly. Technician B states that a defective metering valve could cause grabby front brakes. Who is correct?
   1. Technician A
   2. Technician B
   3. Both A and B
   4. Neither A nor B

8. A vehicle comes into the shop with a red brake warning light illuminated. Technician A states that the parking brake could be applied or malfunctioning. Technician B states that there could be unequal pressure in the hydraulic brake system. Who is correct?
   1. Technician A
   2. Technician B
   3. Both A and B
   4. Neither A nor B

9. A brake booster is being discussed. Technician A states that most diesel vehicles are equipped with brake boosters that utilize the engine’s intake manifold vacuum. Technician B states that the purpose of the brake booster diaphragm is to allow air to be evacuated from the booster, but not to return. Who is correct?
   1. Technician A
   2. Technician B
   3. Both A and B
   4. Neither A nor B

10. A hydraulic brake booster is being discussed. Technician A states that a broken power steering belt could cause the brake booster to stop creating brake assist. Technician B states that some hydraulic brake boosters use an electric motor to create hydraulic pressure for the booster. Who is correct?
    1. Technician A
    2. Technician B
    3. Both A and B
    4. Neither A nor B

Assignments

• Review all materials from this chapter and be prepared for a chapter quiz to be administered (date to be determined by instructor).
• Direct students to read the next chapter in Fundamentals of Automotive Maintenance and Light Repair, Second Edition as listed on your syllabus to prepare for the next class session.

Chapter 31

Principles of Braking

Learning Objectives

After reading this chapter, you will be able to:

• 31-01 Describe the history of brake development.
• 31-02 Describe braking fundamentals.
• 31-03 Describe the physics of braking.
• 31-04 Describe friction, heat transfer, and brake fade.
• 31-05 Describe rotational force, weight transfer, and levers.
• 31-06 Describe the common types of automotive brakes.

ASE Education Foundation Tasks

The following ASE Education Foundation Automobile Accreditation Tasks are covered in this chapter:

• VA4 Identify brake system components and configuration.

Readings and Preparation

• Review all instructional materials, including the chapter in Fundamentals of Automotive Maintenance and Light Repair, Second Edition, and all related presentation support materials.

Support Materials

• Lecture PowerPoint presentation, including all Skill Drills

Pre-Lecture

• You Are the Automotive Technician
  • A progressive case study that encourages critical thinking skills.
  • Direct students to read the “You Are the Automotive Technician” scenario found at the beginning of each chapter.
  • Group Activity: Direct students to review the discussion questions at the end of the scenario and prepare a response to each question. Facilitate a class discussion centered on the questions.
  • Homework Assignment: Ask students to turn in their comments on the questions.
• Teaching Tip: Explain to students how this material applies to the workplace. Provide an example of a situation to make it relevant and meaningful. How does it fit into the broader picture? Is it building on something they already know? Will it help them master a skill? Students need to understand that what we are teaching is of importance on the job. This can be done by describing interesting braking system repairs you have experienced. You can also have students complete the online pre-test for this chapter in the CDX online system. This will help them understand what they do and do not know about the braking system.

Lecture

31-01 Describe the history of brake development.

• Scrub brakes are a simple mechanical system that use leverage to force a friction block against one or more wheel.
• Band brake uses a metal band lined with friction material to clamp around the outside of a drum mounted to the axle or wheel.
• The drum brake consists of two brake shoes that push against the inside of the brake drum.
• Disc brakes force brake pads against the outside of the brake rotor.
• The first versions of EBC systems were the antilock brake systems (ABS).
• ABSs use a computer to monitor each wheel’s speed during braking.
• Additional safety demands led to the development of two major enhancements to ABS: traction control systems (TCS) and electronic stability control (ESC).
• EBC systems have been further enhanced with features such as brake assist (BA), which give greater control of the braking system to the computer.
• A full brake-by-wire system does away with the hydraulic portion of the brake system.
• The driver applies foot pressure to a brake pedal emulator, which tells the computer how firmly the driver intends to brake.
• The regenerative braking system uses the electric motor as a generator; instead of applying friction brakes and losing energy as heat, the generator slows the vehicle by changing the vehicle’s kinetic energy into electrical energy.

31-02 Describe braking fundamentals.

• There are two brake systems on all vehicles: the service brake is used for slowing or stopping the vehicle when it is in motion; the parking brake is used for holding the vehicle in place when it is stationary.
• Modern braking systems are hydraulically operated and have two main sections: the brake units and the hydraulic system that applies them.
• In disc brakes, pads are forced against the outside of a brake disc.
• An effective braking system is designed so it will function in various conditions of all the following situations:
  • Road surface
  • Road conditions
  • Weight of the vehicle
  • Load on the wheel during stoppings
  • Height of the vehicle
  • How the vehicle is being driven
  • The tires on the vehicle

31-03 Describe the physics of braking.

• Kinetic energy is the energy of an object in motion.
• During braking, the kinetic energy in the moving vehicle is converted to heat energy, which is a function of the braking system.
• Newton’s first law of motion states that an object will stay at rest or uniform speed unless it is acted upon by an outside force.
• Acceleration refers to an increase in an object’s speed.
• Deceleration refers to a decrease in an object’s speed.
• When the driver steps on the throttle pedal, the engine’s power output is increased, and the vehicle accelerates.
• The force of the brakes absorbs the kinetic energy of the vehicle as it brakes.
• The law of conservation of energy states that energy cannot be created or destroyed.

31-04 Describe friction, heat transfer, and brake fade.

• Brakes transform kinetic energy to another form of energy.
• Friction is the resistance created by surfaces in contact.
• The amount of friction between two surfaces in contact with each other is expressed as a factor, called the coefficient of friction.
• Ultimately, most of the heat generated by the braking process radiates into the atmosphere; how it does this depends on the type of braking system.
• Brake fade is the reduction in stopping power in the brake system.
• Heat fade is caused by the buildup of heat in the braking surfaces.
• Heat transfer is used to move heat away from the friction surfaces and allow them to continue generating heat.
• The second type of brake fade is called water fade and is caused by water-soaked brake linings.
• The third kind of brake fade is called hydraulic fade and is caused by the brake fluid becoming so hot that it boils.

31-05 Describe rotational force, weight transfer, and levers.

• When brakes are operated on a moving vehicle, a rotational force is generated in the brake and suspension components.
• Friction between the brake components tends to twist the brake support in the direction of wheel rotation.
• Another result of rotational force is weight transfer, where the weight is transferred to the front wheels.
• Weight transfer causes the front wheels to have increased traction during braking.
• Brake systems use levers and mechanical advantage to apply service and parking brakes.
• The point around which a lever rotates and that supports the lever and the load is called the fulcrum.
• Mechanical disadvantage is when the load distance is greater than the effort distance, and the effort required is greater than the load being moved.
• Types of levers: lever of the first order, lever of the second order, and lever of the third order.

31-06 Describe the common types of automotive brakes.

• Each vehicle application lends itself to a particular type of brake system.
• Hydraulically operated friction brakes use two kinds of wheel brake units.
• Drum brakes have a drum attached to the wheel hub and rotate with the tire.
• Disc brakes have a disc brake rotor attached to the wheel hub and rotate with the tire.
• Modern drum and disc brake systems are regularly fitted with an ABS, which includes a brake pedal, power booster, master cylinder, wheel speed sensors, the ECU, and the hydraulic control unit, also called a hydraulic modulator.
• There are several types of parking brakes.
• In a top hat parking brake design, the vehicle is equipped with disc brakes that incorporate a mechanically operated drum-style parking brake.
• In a disc brake with integral parking brake, the brake pads are mechanically applied by a parking brake cable.
• On drum brakes, a drum-style parking brake mechanically applies the brake shoes against the drum.
• A transmission-mounted parking brake uses a small drum brake mounted between the transmission and drive shaft.
• Parking brake cables transmit force from the parking brake actuating lever to the brake unit.
• Parking brakes are commonly applied in two ways: hand-operated lever, usually mounted between the front seats; and a foot-operated mechanism.
• When adjusting parking brakes, the order of adjustment is as follows:
• The parking brake cable, which should have slack in it
• The service brakes, which are adjusted according to the manufacturer’s procedure
• The parking brake

Post-Lecture

This section contains various student-centered end-of-chapter activities designed as enhancements to the instructor’s presentation. As time permits, these activities may be presented in class. They are also designed to be used as homework activities.

1. Direct students to read and individually answer the question sets located in the Wrap-Up section at the end of each chapter. Allow approximately 10–20 minutes for this part of the activity.
2. Facilitate a class review and discussion of the answers, allowing students to correct responses as may be needed. Use the answers noted in the Answer Key to assist in building this review.
3. You may wish to ask students to complete this activity on their own and turn in their answers on a separate piece of paper.

Review Questions

This question set is designed to assist students in understanding the chapter content by asking knowledge-based comprehension questions.

1. What was the primary reason for the development of hydraulic braking?
   1. To equalize braking forces at each wheel and prevent brake pull
   2. To make brake pads and shoes last longer
   3. To dissipate heat better preventing brake fade
   4. To increase the amount of force required at the brake pedal

2. All of these are factors that influence braking, EXCEPT:
   1. vehicle weight.
   2. tire condition.
   3. road condition.
   4. TCS disabled.

3. What system helps the driver apply the brakes by increasing the force applied to the master cylinder?
   1. Power booster
   2. Regenerative braking
   3. Brake-by-wire
   4. Band brakes

4. If a moving vehicle doubles its speed, its kinetic energy:
   3. is squared.
   4. is multiplied by π.

5. Why is heat transfer important to braking systems?
   1. Heat transfer to the brake fluid must be increased to keep it from boiling.
   2. Heat transfer must be increased to allow the brake linings to heat up properly.
   3. Heat transfer traps heat in the rotor to enhance braking performance.
   4. Heat transfer allows air to remove heat from the brakes to prevent heat fade.

6. What are the symptoms of hydraulic fade?
   1. Dragging rear brakes
   2. Grabbing front brakes
   3. Spongy and low pedal
   4. Steering wheel vibration

7. What force causes the rear of a vehicle to lift during braking?
   1. Clamping force
   2. Spring force
   3. Rotational force
   4. Centrifugal force

8. Weight transfer causes:
   1. spongy pedal.
   2. low brake fluid level.
   3. increased traction.
   4. hydraulic fade.

9. What are the two most common types of parking brake mechanisms?
   1. Hydraulic and pneumatic
   2. Hand lever and foot pedal
   3. Kinetic and potential
   4. Heat fade and water fade

10. How are park brakes commonly adjusted?
    1. Adjusting nuts on the cables
    2. Rotating an eccentric at the hand lever
    3. Applying the service brakes in reverse
    4. Topping off the master cylinder reservoir

ASE Technician A/Technician B Style Questions

This question set is designed to assist students in gaining a further understanding of and familiarity with ASE Technician A/Technician B questions.

1. Technician A says that an ABS prevents wheel lockup during hard braking. Technician B says that a TCS prevents tires from losing traction during acceleration. Who is correct?
   1. Technician A
   2. Technician B
   3. Both A and B
   4. Neither A nor B

2. Technician A says that brake-by-wire systems use braided steel cables instead of fluid to apply the brakes. Technician B says that regenerative braking uses friction to regenerate braking power. Who is correct?
   1. Technician A
   2. Technician B
   3. Both A and B
   4. Neither A nor B

3. Technician A says that parking brakes are designed to stop a vehicle in an emergency. Technician B says that service brakes are used to slow and stop a vehicle safely. Who is correct?
   1. Technician A
   2. Technician B
   3. Both A and B
   4. Neither A nor B

4. Technician A says that a vehicle changes chemical energy (in the form of gasoline or diesel) into kinetic energy (in the form of acceleration and speed). Technician B says that a vehicle’s brake system changes kinetic energy (in the form of speed) into heat energy through friction. Who is correct?
   1. Technician A
   2. Technician B
   3. Both A and B
   4. Neither A nor B

5. Technician A says that a higher coefficient of friction typically results in less wear of the brake lining material. Technician B says that friction between the tire and road surface is sometimes referred to as traction. Who is correct?
   1. Technician A
   2. Technician B
   3. Both A and B
   4. Neither A nor B

6. Technician A says that water fade changes the coefficient of friction between the brake linings and drums until they dry out. Technician B says that hydraulic fade is caused by brake caliper seals leaking fluid onto the rotors. Who is correct?
   1. Technician A
   2. Technician B
   3. Both A and B
   4. Neither A nor B

7. Technician A says that the pivot point of a brake pedal lever can be referred to as the fulcrum. Technician B says that leverage is a form of mechanical advantage. Who is correct?
   1. Technician A
   2. Technician B
   3. Both A and B
   4. Neither A nor B

8. Technician A says that the size of the master cylinder pistons does not affect braking. Technician B says that valves may be used during hard braking to keep wheels from locking up. Who is correct?
   1. Technician A
   2. Technician B
   3. Both A and B
   4. Neither A nor B

9. Technician A says that disc brakes use friction linings attached to brake pads. Technician B says that disc brakes are mechanically operated. Who is correct?
   1. Technician A
   2. Technician B
   3. Both A and B
   4. Neither A nor B

10. Technician A says that drum brakes expand linings against a rotor to slow the vehicle. Technician B says that the power brake booster reduces the amount of force applied to the master cylinder. Who is correct?
    1. Technician A
    2. Technician B
    3. Both A and B
    4. Neither A nor B

Assignments

• Review all materials from this chapter and be prepared for a chapter quiz to be administered (date to be determined by instructor).
• Direct students to read the next chapter in Fundamentals of Automotive Maintenance and Light Repair, Second Edition as listed on your syllabus to prepare for the next class session.