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 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.