Chapter 28

Suspension Systems Theory

Learning Objectives

After reading this chapter, you will be able to:

• 28-01 Describe suspension system principles.
• 28-02 Describe suspension system spring components.
• 28-03 Describe fixed shock absorbers and struts.
• 28-04 Describe manually and automatically adjustable shocks.
• 28-05 Describe suspension system components.
• 28-06 Describe the main types of suspensions.
• 28-07 Describe the main types of front suspension
• 28-08 Describe the main types of rear suspension systems.
• 28-09 Describe active and adaptive suspension systems.

ASE Education Foundation Tasks

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

chapter:

• IVA3 Identify suspension and steering system components and configurations.
• IVB23 Describe the function of suspension and steering control systems and components (i.e., active suspension and stability control).

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 some interesting faults in a suspension system you have seen. 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 suspension systems.

Lecture

28-01 Describe suspension system principles.

• The suspension system of a vehicle is designed to keep the tires in contact with the road surface, while isolating the passengers from it.
• Wear from extended use is the main cause of suspension problems, in addition to impact from potholes and accidents.
• There are several driver complaints that indicate problems in the suspension system.
• The suspension system reduces road shocks.
• When a tire hits a bump, it creates a reaction force.
• The size of the reaction force generated depends on the unsprung mass, also called unsprung weight.
• Sprung weight is the body, drivetrain, and associated parts that are supported by the springs.
• The heavier the unsprung components, the greater the reaction force they will generate.
• If the unsprung weight is very light, it will not generate as much upward reaction force.
• Suspension systems must absorb the large road forces generated while driving on imperfect roads.
• The suspension system has to support the weight of the vehicle, occupants, and any additional load.
• The suspension system has elasticity that allows it to flex and return to its original shape.
• There are three primary types of springs used in suspension systems: leaf springs, coil springs, and torsion bars.
• Leaf springs are located between the frame and the axle assemblies and absorb the applied force (pressure of the load) by flattening out under load.
• Coil springs are formed in a spiral from a single steel rod.
• Torsion bars are straight bars that return to their original shape when the deflecting force is removed.
• Nonmetallic materials, such as rubber, provide cushioning action; they are more commonly used as stops to limit extreme suspension movement.
• In some light vehicle applications, air is used for ride height control.
• When springs are supporting the weight of the vehicle, they are in a partially compressed condition.
• Oscillations means the spring compresses and rebounds over and over again.
• When a vehicle is in motion, driving thrust, braking torque, and cornering force exert pressure against the wheel units.
• Driving thrust is the force transferred from the tire contact patch through the wheel.
• Braking torque also places a twisting force on the suspension system.
• Cornering force refers to the lateral movement of the suspension system during turning.
• The terms “yaw,” “pitch,” and “roll” describe the movement of a vehicle around three axes.
• Roll is vehicular movement along its x-axis; pitch is movement around the vehicle’s y-axis; and yaw is movement around the z-axis, felt when the vehicle deviates from its straight path.

28-02 Describe suspension system spring components.

• A basic suspension system consists of springs, axles, shock absorbers, control arms, rods, and ball joints.
• Rebound clips are metal straps wrapped at intervals around the leaf spring.
• The longest leaf, called the main leaf, is rolled at both ends to form spring eyes.
• Some multi-leaf springs have the ends of the second leaf rolled around the eyes of the main leaf as reinforcement This leaf is called the wrap leaf.
• Torsion bars can be used across the chassis frame in a trailing arm suspension.
• A bar similar to the torsion bar is the sway bar, or antiroll bar.

28-03 Describe fixed shock absorbers and struts.

• A shock absorber is a device designed to dampen spring oscillations.
• Most direct-acting telescopic shock absorbers are of the twin-tube type.
• A strut functions exactly like a shock absorber, but it is much stronger because it is a structural part of the suspension system.
• In a gas shock, pressure on the oil is provided by nitrogen gas at the base of the cylinder.

28-04 Describe manually and automatically adjustable shocks.

• To better handle extra loads, a manually adjustable air spring can be incorporated into the shock absorbers.
• This type of shock absorber is commonly referred to as an air shock.
• The air spring consists of a flexible rubber bladder, which seals the outside of the upper and lower halves of the shock absorber.
• Another type of load-adjustable shock absorber uses a coil spring around the outside of the shock.
• A manual adjustable-rate shock absorber has a manual, external damper rate adjustment.
• Some vehicles are equipped with electronic ride control systems that provide driver-selected control of the ride quality.
• Electronic ride control can also be automatic, with no provision for driver control.
• Another type of electronically adjustable shock is the solenoid-controlled shock.
• The newest style of electronically adjustable shock uses a special type of fluid called magneto-rheological fluid.
• Automatic load-adjustable shock absorbers are also called self-leveling.

28-05 Describe suspension system components.

• Control arms are components that serve as a primary load-bearing element of a vehicle’s suspension system.
• Control arms can be formed in different shapes.
• The A-arm style is sometimes referred to as a wishbone control arm.
• Another type of control arm uses only one contact point at the frame or body.
• Rods are typically straight (or precisely formed) pieces of steel used to either transfer motion or prevent motion within a vehicle’s suspension system.
• A suspension system may use tie rods, lateral rods, tension rods, control rods, Panhard rods (track bars), steering track rods, or strut rods.
• The steering knuckle, also known as a stub axle or spindle assembly, can be found in many variations.
• One type uses a forged piece containing the wheel hub or spindle and attaches to the suspension components.
• Ball joints are swivel connections mounted in the outer ends of the control arms that allow the steering knuckle to pivot.
• Ball joints are typically constructed of a ball and socket.
• A ball joint is made up of a pressed-steel housing fitted with sintered iron seats.
• The ball joints can be designed to primarily carry either compression loads or tension loads.
• Bushings act as pivot points and cushions at suspension fulcrum points.
• They allow for limited movement of the component while maintaining its alignment.
• Spring shackle bushings can be molded to form two halves.
• Rubber-bonded bushings are normally used for the front eye of the spring at the fixed shackle point.

28-06 Describe the main types of suspensions.

• Manufacturers use various types of suspension systems depending on the intended use of the vehicle, cost of manufacturing, and layout of the drivetrain.
• Suspension systems are designed to maintain the proper positioning of the wheels during all driving conditions.
• The terms dead axle and live axle refer to whether the axle is a driving axle or not.
• A dead axle simply holds the wheels in their proper orientation; a live axle not only holds the wheels in position but also drives them.
• The solid axle (beam axle) provides a simple means of mounting the hub and wheel assembly.
• A solid axle forms a dependent suspension because the wheels on both sides of the axle are connected.
• An independent suspension allows the wheel on each side of the axle to move up and down independently of the other.
• One of the main benefits claimed for independent suspension is that unsprung mass can be kept low.

28-07 Describe the main types of front suspension systems.

• The front suspension must accommodate steering and mostly incorporates a sway bar.
• The two main types of front suspension systems are the independent and the solid axle systems.
• In strut suspension, the shock absorber is contained inside the strut.
• The modified strut system uses one control arm with the strut mounted in the same manner as a MacPherson strut.
• The double-wishbone modified strut suspension uses a high-mount upper arm.
• The SLA suspension gets its name from using two different-length control arms: one short upper control arm and one long lower control arm.
• The twin I-beam suspension is a type of independent suspension; for each front wheel, it uses separate I-beams.

28-08 Describe the main types of rear suspension systems.

• The main function of the rear suspension system is to keep the rear tires in contact with the road, but they also must maintain their alignment with the front tires.
• Rear-wheel suspension systems can be of either the independent or solid axle design.
• A rigid-axle leaf-spring suspension can be used in both dead axles and live axles; the front of the leaf spring is attached to the chassis at the rigid spring hanger.
• In rigid-axle coil-spring suspensions, the coil spring is mounted between the axle housing and the vehicle body.
• The first style uses lower control arms near each coil spring that are parallel with the centerline of the vehicle.
• A Panhard rod, also referred to as a track bar, sits parallel with the axle.
• A Watt’s linkage is a bit more complex but functions in a similar way.
• A rigid dead axle is sometimes referred to as a beam axle. It can come in a variety of configurations; with rigid dead axle suspension, the longitudinal and lateral position of the axle must be maintained as in all axles.
• The kind of dead independent suspension used on the rear of a vehicle can be fairly simple; the suspension system only has to hold the wheels in the proper orientation while the vehicle is being driven.
• In rear-wheel drive vehicles with independent rear suspension, the final drive unit is attached to the vehicle frame.
• Drive is transmitted to each wheel by external driveshafts.
• The final drive assembly is normally bolted to the chassis. When universal joints are used, each driveshaft may have a splined section called a slip joint.

28-08 Describe active and adaptive suspension systems.

• There are two main categories of suspension system control: active and adaptive (also called semi-active).
• An active suspension system acts independently of the driver; it fully controls the actions of each individual wheel while the vehicle is being driven.
• Adaptive air suspension systems are less sophisticated than active systems.

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. All of the following are significant functions of a vehicle’s suspension system, EXCEPT:
   1. To keep tires in contact with the road surface
   2. To keep the vehicle body firmly mounted to the frame
   3. To maintain traction and control of the vehicle
   4. To provide a smooth ride for passengers

2. Which type of spring is often held together by a center bolt and attached to a rear axle by a U-bolt?
   1. Coil springs
   2. Torsion bars
   3. Sway bars
   4. Leaf springs

3. Which component is primarily responsible for dampening oscillations?
   1. The coil springs
   2. The torsion bars
   3. The sway bar
   4. The shock absorbers

4. On a MacPherson strut suspension design, what does the bottom of the strut connect to?
   1. The steering knuckle
   2. The ball joint
   3. The tie-rod end
   4. The wheel flange

5. In a load-adjustable shock absorber, why would an internal air spring be incorporated?
   1. To adjust the dampening action when going over bumps
   2. To support additional weight and adjust ride height
   3. To give it a stiff sporty feel on winding roads
   4. To make the steering more responsive to the driver

6. What is another common name for a steering knuckle?
   1. Tie rod
   2. Steering pinion
   3. Steering track rod
   4. Spindle assembly

7. When a solid rear axle simply supports the rear wheels without transmitting power to the wheels, what is it called?
   1. A live axle
   2. An independent axle
   3. A dead axle
   4. A drive axle

8. Which of the following is NOT a type of independent front suspension?
   1. Short long arm (SLA)
   2. Solid axle
   3. Double wishbone
   4. Twin I-beam

9. On a rear solid axle suspension, what part is mounted parallel to the axle, connecting the axle to the frame to control side-to-side axle movement?
   1. Leaf springs
   2. Coil springs
   3. Trailing arms
   4. Panhard rod

10. On an adaptive air suspension, how is a vehicle lowered?
    1. The air pump is cycled off and air travels back through the pump.
    2. The air is directed from the rear shocks to the front.
    3. An exhaust valve is opened until the desired height is achieved.
    4. The isolation valve is opened, diverting air into the desired shock.

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 vehicle comes into the shop for a suspension inspection. Technician A states that the suspension should be inspected for wear and looseness from normal use. Technician B states that the suspension should be inspected for bent or damaged components due to impacts such as potholes or accidents. Who is correct?
   1. Technician A
   2. Technician B
   3. Both A and B
   4. Neither A nor B

2. A vehicle with torsion bar suspension comes into the shop with a low ride height. Technician A states that springs can wear and eventually start to sag. Technician B states that some torsion bar suspensions have an adjustment, which may return the vehicle back to its original ride height. Who is correct?
   1. Technician A
   2. Technician B
   3. Both A and B
   4. Neither A nor B

3. A vehicle is being inspected and is found to have oil on the bottom of a shock absorber. Technician A states that this could indicate a leaking shock absorber which could affect ride quality. Technician B states that the oil level in the shock absorber should be checked and topped off if necessary. Who is correct?
   1. Technician A
   2. Technician A
   3. Both A and B
   4. Neither A nor B

4. A high-performance sports car is being discussed. Tech­nician A states that its adjustable shock absorbers may be controlled by externally mounted knobs that adjust fluid passage size. Technician B states that the adjustments may be electronic and controlled by a selector in the passenger compartment. Who is correct?
   1. Technician A
   2. Technician B
   3. Both A and B
   4. Neither A nor B

5. Suspension components are being discussed. Technician A states that ball joints are also known as stub axles. Technician B states that ball joints may have a grease fitting which allows for periodic lubrication. Who is correct?
   1. Technician A
   2. Technician B
   3. Both A and B
   4. Neither A nor B

6. Suspension types are being discussed. Technician A states that most rear-wheel-drive vehicles are equipped with a dead axle. Technician B states that most trailers are equipped with a live axle. Who is correct?
   1. Technician A
   2. Technician B
   3. Both A and B
   4. Neither A nor B

7. Front suspension types are being discussed. Technician A states that a MacPherson strut design utilizes upper and lower control arms. Technician B states that an SLA type utilizes upper and lower ball joints. Who is correct?
   1. Technician A
   2. Technician B
   3. Both A and B
   4. Neither A nor B

8. A vehicle with a double wishbone front suspension comes into the shop for maintenance. Technician A states that there are two lower control arms and no upper control arms. Technician B states that there are no upper ball joints, so only the lower ball joints should be inspected and serviced. Who is correct?
   1. Technician A
   2. Technician B
   3. Both A and B
   4. Neither A nor B

9. Rear suspension systems are being discussed. Technician A states that some rear-wheel-drive vehicles are equipped with an independent rear suspension. Technician B states that some rear suspension systems are MacPherson strut design. Who is correct?
   1. Technician A
   2. Technician B
   3. Both A and B
   4. Neither A nor B

10. Active and adaptive suspension systems are being discussed. Technician A states that active systems can respond to changes while driving. Technician B states most adaptive air suspension systems receive information from sensors mounted on the suspension. 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 26

Steering Systems Theory

Learning Objectives

After reading this chapter, you will be able to:

• 26-01 Describe steering system preliminaries.
• 26-02 Describe steering geometry and rack-and-pinion layout.
• 26-03 Describe parallelogram steering layout.
• 26-04 Describe steering columns and their components.
• 26-05 Describe rack-and-pinion steering boxes.
• 26-06 Describe worm gear steering boxes.
• 26-07 Describe hydraulic power steering system operation.
• 26-08 Describe electric power steering system operation.
• 26-09 Describe four-wheel steering operation.

ASE Education Foundation Tasks

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

• IVA3 Identify suspension and steering system components and configurations.

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 some interesting faults in a steering system you have seen. You can also have students complete the online pre-test for this chapter in the CDX Online course. This will help them understand what they do and do not know about steering systems.

Lecture

26-01 Describe steering system preliminaries.

• A basic steering system has four main assemblies: a steering column, a steering box, a steering linkage, and steering knuckles.
• The power assist system makes it easier for the driver to steer the vehicle and can be either hydraulic type or electric type.
• The steering column transmits the driver’s steering effort from the steering wheel to the steering box.
• The steering box converts the rotary motion of the steering wheel into the lateral motion required to pivot the wheels. It uses gear reduction to give the driver mechanical advantage over the wheels, making them easier to steer.
• The steering linkage transfers the linear steering effort to the wheels by connecting the steering box to the steering arm on each of the steering knuckles.
• The rack-and-pinion gear uses a rotating pinion to move a flat-toothed rack, which is connected through pivoting socket ends and a tie rod directly to the steering arms.
• It is a simple and compact system that fits in most engine compartments and takes up less space than other systems. It has few moving parts and is less likely to get in the way of other components while giving a more precise and responsive steering feel due to the orientation of the pinion gear to the rack.
• In the parallelogram steering system, the center link and axle, along with the pitman arm and idler arm, always move parallel to each other.
• Parallelogram steering uses a worm gearbox to provide mechanical advantage and change the direction of rotation by 90 degrees.
• The worm gear reduces road shock transmitted to the steering wheels, making it useful in off-road four-wheel drive vehicles and non-sporty vehicles.
• The pitman arm and center link turn the rotary motion into lateral motion.
• The steering knuckles connect the wheels to the suspension and steering components and pivot on one or two ball joints depending on the type of suspension.
• Some knuckles provide a stub axle on which the wheel bearings ride, and some use a hub-style wheel bearing assembly that is pressed or bolted to the steering knuckle.

26-02 Describe steering geometry and rack-and-pinion layout.

• Steering geometry refers to the geometric arrangement of the linkages in the steering system, which is designed to keep the wheels properly oriented through the movement of the steering and suspension system.
• When rounding a corner, the inner and outer wheels must trace circles of different radii or the tires would be dragged across the road surface, which is called scrub.
• When turning in either direction, the inside wheel must always turn more sharply than the outside wheel, and is called toe-out on turns.
• The Ackermann principle affects the angle of the steering arms on the steering knuckles, which are angled toward the center of the vehicle.
• Imaginary lines drawn from the center of the outer tie rod ends intersect at the center of the rear axle, allowing the front wheels to navigate a corner around a common center point, which minimizes scrub.
• The rack-and-pinion steering is used on the majority of vehicles and has very little sliding and rotational resistance, which gives lighter operation.
• The pinion is a toothed helical gear that meshes with the rack and is connected to the steering column.
• The rack is a toothed, straight piece of metal that has tie rods at each end that fasten to the steering knuckle.
• An adjustable or spring-loaded bushing opposite the pinion controls the component’s meshing while the rack rides on a nylon bushing at the other end.
• The inner tie rod has an inline ball-and-socket joint that threads onto one end of the rack and is threaded at the other end into the outer tie-rod end.
• These two joints allow for suspension and steering angle movement while the tie rod is free to spin in the ball and socket when making adjustments to wheel alignment.
• The outer tie-rod end is attached between the inner tie-rod shaft and the steering arm and transfers the movement of the rack to the steering arm.
• A jam nut locks the shaft and outer tie rod in place while allowing the tie rod to be adjusted when making wheel alignment adjustments.
• Rubber bellows protect the inner joints from dirt and contaminants while retaining grease lubricant inside the rack-and-pinion housing.
• Each end of the rack contains similar bellows.

26-03 Describe parallelogram steering linkage.

• The parallelogram steering linkage is used where ride comfort is more important than sporty handling, such as in larger vehicles, and is more complicated than rack-and-pinion steering.
• The pitman arm transfers movement from the steering box to the center link and is attached to the steering box by a spline and nut.
• The idler arm is attached to the chassis and is positioned parallel to the pitman arm. It is the pivoting support for the steering linkage with a pivot on one end and a ball socket on the other.
• The idler arm is attached between the center link, on the opposite side of the pitman arm, and the vehicle frame. It holds the center link at the proper height to accurately relay the pitman arm’s movement.
• The center link is also called the track rod or drag link and applies any movement in the pitman arm to the idler arm.
• Tie rods connect the center link to the steering arms and use pivoting tie-rod ends at each end to allow the steering linkage to move only as needed.
• Tie-rod ends are attached to each end of the tie-rod shaft and serve as pivot points as the steering linkage is extended and retracted during turns.
• Tie rods and tie-rod ends are left- or right-hand threaded, and when used with an adjustment sleeve allows the length of the tie rod to be adjusted.
• The adjustment sleeve connects the tie rods to the tie-rod ends and provides the adjustment point for adjusting toe settings.
• When the sleeve is turned, the tie rod lengthens or shortens, which is used to adjust the wheel alignment.
• Each connection in the steering linkage system has a flexible joint that is usually a ball-and-socket joint that allows for steering and suspension movement.
• Bump steer is the undesired condition produced when a vehicle darts to one side if it hits a bump.
• This is caused when the steering linkage is pulled to one side because of suspension travel and is usually due to a bent or wrong steering system component.
• If the angles between the steering system and suspension do not match, going over a bump will cause one or both wheels to change direction.
• In four-wheel drive vehicles with a beam axle, a single tie rod may connect the steering arms on each wheel assembly.
• Movement of the pitman arm is transferred through the drag link to one of the wheels, and the tie rod transfers the movement to the other wheel.
• Four-wheel drive vehicles of this type typically use a steering damper mounted between the tie rod and either the rigid axle or the vehicle frame to prevent shock forces from being transferred through the steering linkage and to the steering wheel.

26-04 Describe steering columns and their components.

• A straight steering shaft can cause serious injury to the driver in a frontal collision because the steering wheel would be forced back toward the driver’s head and chest.
• Steering columns are fitted with collapsible sections to protect the driver.
• During a collision, the steering column is forced toward the driver, and plastic shear pins allow the lower shaft to slide over the upper shaft. The mass of the driver striking the steering wheel breaks the brackets on the upper part of the column and drives it into the lower column.
• Some steering columns use an intermediate shaft that runs at an angle from the steering column to the steering gear, allowing it to fold in case of a collision and preventing the impact force from being transmitted directly to the column.
• A flexible joint is used to connect the steering column to the input shaft of the steering gear because the steering column sits at an angle to the steering box, and it reduces the transmission of road shocks to the driver.
• An electric motor and sensors may be fitted to the steering column to provide information to the steering control module and the electronic stability control system or to provide power steering assist.
• The steering column generally accommodates several controls: a horn button, an ignition switch and lock assembly, a multifunction switch or separate switches for lights, turn indicators, wipers, a washer, cruise control, and steering integrated control switches for the entertainment system, cell phone control, and instrument display panel options.
• Tilting and/or telescoping mechanisms are added to steering columns to allow drivers to adjust the steering wheel position, so it best suits their needs.
• The tilt mechanism uses a heavy spring, a pivot joint, and ratchet mechanism. The telescoping mechanism uses a slip joint and locking mechanism.
• These features tend to put additional stress on the wires in the steering column and makes it more complicated to repair.
• The driver’s side air bag provides a collapsing cushion that decelerates a driver’s head and chest in a collision and prevents it from contacting the steering wheel or dash.
• Airbag replacement is part of the collision repair process and it may be legally required to replace the airbag and cover if it has been deployed in a collision.
• Manufacturers may have further requirements that specific components be inspected or replaced along with airbags.
• The clock spring, also called a spiral cable, is a special rotary electrical connector that is used to connect the steering-mounted airbag to its control module.
• It maintains a constant electrical connection with the wiring as it coils and uncoils when the steering wheel is being turned.
• When removing the airbag assembly from the steering wheel, the cock spring should be inspected and replaced if damaged.

26-05 Describe rack and pinion steering boxes.

• Steering boxes are either manually operated or power assisted and may have rack-and-pinion gearing or use worm gearing and a sector shaft.
• Common variations of steering boxes are the rack-and-pinion, or a worm gearbox consisting of worm and sector, worm and roller, or worm and nut, which is also referred to as the recirculating ball style.
• A rack-and pinion gearbox has a pinion gear that is turned by the steering wheel, which meshes with a rack that is connected to the tie rods.
• On end take-off racks, ball sockets are mounted to the end of the rack, whereas on center take-off racks the tie rods connect to the center of the rack-and-pinion assembly.
• The steering gears on the rack-and-pinion are helical and also provide a mechanical advantage determined by the gear ratio.
• Rack-and-pinion systems may be fixed ratio, where a single ratio reduction is produced from lock to lock, or variable ratio, which can allow for a slower or faster turn rate depending on whether the pinion is at the center or at the end of the rack.
• The rack-and-pinion system is not usually adjustable and can wear and produce backlash, which is felt as play in the steering wheel.
• The steering rack is supported at the side opposite the pinion by a spring-loaded rack guide yoke made of metal, nylon, or other durable materials.
• The spring pushes on the back of the rack and reduces the play between the rack and pinion while still allowing for relative movement.
• An adjuster plug may be used to put pressure on the rack guide yoke to produce the correct meshing between rack-and-pinion teeth.
• The adjuster plug also affects the torque required to turn the pinion, and overtightening may result in a steering wheel that does not turn properly, sometimes called memory steer.
• It is usually not necessary to adjust the rack-and-pinion mesh.
• The pinion is supported by two preloaded bearings in the rack housing, which hold the pinion in place and eliminates free play.
• The rack-and-pinion steering box is lubricated with grease, and either end is protected with bellows.
• On some assemblies, a tube connects the two rubber bellows and transfers air from the collapsing bellows to the expanding bellows as the rack moves to keep them from collapsing.

26-06 Describe worm gear steering boxes.

• A worm gearbox uses a worm gear with helical teeth and a worm wheel that moves one tooth for every rotation of the worm.
• It produces a large gear reduction and does not transmit as much road shock back to the driver as a rack-and-pinion type gear assembly, as most of the force from the worm wheel is nearly perpendicular to the rotation of the worm gear.
• In the worm-and-sector style gearbox, the worm is meshed with a sector or portion of a gear that is mounted on a sector shaft.
• As the steering wheel rotates, the worm causes the sector to move through an arc. The sector shaft is splined to the pitman arm and transfers the motion to the steering linkage.
• The worm-and-roller gearbox has an hour-glass shaped worm that meshes with a double-ribbed roller.
• As the worm rotates, the roller follows the hour-glass shape and its angle changes, this moves the pitman shaft.
• The shape of the worm changes the steering ratio slightly as the roller nears each end.
• The recirculating ball steering box contains a worm gear inside a ball nut with spiral grooves cut into the worm and the inside of the nut.
• There are many balls that roll in these grooves between the worm and the ball nut as the worm is rotated and cause the nut to thread up and down along the worm.
• When the balls get to the end of the groove, they travel through ball-return guides to the other end of the nut.
• The gear teeth cut into the outside of the ball nut engage a sector shaft, which turns the pitman arm,
• The sector gear and nut teeth are designed to have minimum clearance when the teeth are in the straight-ahead position to reduce free play when the steering is straight.
• The pitman shaft is supported by two caged needle roller bearings in the steering box housing.
• An adjustment mechanism on the steering housing cover allows the sector gear height to be adjusted to ensure proper engagement of the angled sector gear teeth and nut teeth.

26-07 Describe hydraulic power steering system operation.

• Power steering assists the driver in steering the wheels and can be of three types: hydraulically assisted power steering, electrically-powered hydraulic steering, or fully-electric power steering.
• Hydraulically-assisted power steering uses fluid pressurized by an engine-driven hydraulic pump to assist the driver in steering the wheels.
• With the engine running, hydraulic fluid flows continuously from the power steering pump to the steering gear control valve, through the power unit, and back to the pump.
• When assist is needed, the control valve increases pressure to one side of the power unit.
• The power steering system may be used to power hydraulic brake boosters or radiator fans so when working on these systems it is important to understand how they are integrated.
• The power steering fluid must withstand high temperatures and pressures, lubricate the pump and steering gears, preserve system seals and pressure hoses, and be able to flow freely at cold temperatures.
• Because excessive heat can degrade power steering fluid, some vehicles are equipped with a fluid cooler that is usually built into the high-pressure line to cool the fluid before it gets to the steering gear.
• A replaceable fluid filter may be used to collect rubber and metallic parts that may be introduced into the fluid from internal system wear.
• Power steering hoses are made from high-pressure hose material and are flexible to allow some movement between the engine and the chassis.
• These hoses may become weak over time and cause leaks, which are especially dangerous due to the flammable nature of power steering fluid.
• O-rings are used to seal the hoses to the pump and steering gear, and these can wear or leak, requiring replacement of the O-rings.
• A rotary valve on the input shaft of the steering wheel controls the hydraulic pressure.
• When the steering wheel is turned, the valve directs fluid pressure to one side or the other of a piston attached to the steering gear.
• In a rack-and-pinion steering gear, the piston is formed centrally on the steering rack with the rack housing acting as the cylinder, and pressure seals at each end of the cylinder isolating the power section from the rest of the rack and pinion.
• In a recirculating ball steering box, the power piston has an extension formed on one side with teeth that engage on the sector.
• Shaft force produced in either direction is transferred through the teeth.
• The rotary valve consists of an inner member that is attached to the input shaft and a surrounding sleeve member attached to the pinion gear or worm.
• When the steering wheel is turned, both members rotate; however, a torsion bar allows a slight displacement of the inner member in the sleeve, which directs the power steering fluid flow.
• The bar can only twist through a small angle before it contacts a stop on the pinion gear or worm, which acts as a failsafe to provide manual steering when power assistance is not available.
• When the steering is in neutral position, the valve allows fluid to pass to both sides of the power piston and no assistance is provided.
• Assist increases as the torsion bar flexes further and grooves on the inner member allow the fluid flow to be metered between the apply and release passageways.
• When steering at slow speeds, power steering demand will be high and engine speed will be low; if idle speed is not maintained, it could cause stalling.
• A power steering switch or sensor supplies power steering pressure information to the PCM, which can raise or maintain the idle speed to match the pressure demand from the power steering system.

26-08 Describe electric power steering system operation.

• Electric power steering systems may be fully electric or electrohydraulic and have several advantages over conventional hydraulic power steering systems.
• They are less expensive to run, easier to package and install, lighter and more compact, and also react faster to quick steering changes from the driver.
• In electrically powered hydraulic steering (EPHS), a brushless motor is used to drive the pump, which replaces the drive belts and pulleys used to drive the pump.
• The pump only operates on demand and is regulated by an electronic controller to vary pump pressure and flow.
• An EPHS system uses only about 20% of the engine power used by standard belt-driven pumps, which improves fuel mileage substantially.
• Electrically assisted steering (EAS) is a fully electric power steering (EPS) system and uses an electric motor to provide assist.
• It eliminates all hydraulic components and fluid and requires only 2% of the engine power used by belt-driven power steering pumps.
• It may be attached to the steering rack or steering column via a gear mechanism and incorporates a microprocessor or electronic control unit to control the steering dynamics and driver effort, using inputs such as vehicle speed, steering wheel torque, angular position, and turning rate.
• There are four primary types of electric power assist steering systems depending on where the power assist unit is attached. They may be column assist type, pinion assist type, rack assist type, or direct-drive type, where the rack-and-pinion and power assist unit form a single unit.
• Active control provides constant feedback from sensors to the control unit, allowing the steering system to react to the road, weather, and even the type of driver.
• The steering sensor is located on the input shaft and performs two functions: a steering torque sensor converts steering torque input into voltage signals while a rotation sensor converts the rotation speed and direction into voltage signals.
• An ECU converts the voltage signals into signals that a PCM can process, after which the PCM outputs the proper signal to the EPS motor.
• The PCM also analyses input from the wheel speed sensors and compares them to the stored forces capability map data to send the appropriate command to the power unit, which supplies the motor with the necessary current to operate as needed.
• The direction of rack movement depends on the direction of flow of electric current, and increasing the current increases the power assist.
• The EPS system has three operating modes: normal control mode provides left or right assist in response to input from the torque and rotation sensor, return control mode assists steering return after completing a turn, and damper control mode, which adjusts the amount of assist according to vehicle speed to improve road feel and dampen kickback.
• The power unit reduces current to the electric motor when the steering is held in full-lock position to prevent overload and also protects the motor from voltage surges from the power system.
• The electronic control unit is capable of self-diagnosing faults by monitoring inputs and outputs and can turn the system off by actuating a fail-safe relay in the power unit, eliminating all power assist and illuminating a warning light to warn the driver.
• In hybrid vehicles, the high-voltage battery usually provides all the power needed for the power steering motor with no reliance on engine or hydraulic power.
• Such vehicles may use a conventional 12-volt system, a mid-range 25–30 volt system, or a higher 46-volt system.
• If higher voltages are used, the high voltage system is usually live when it is operated so adequate safety precautions should be taken.

26-09 Describe four-wheel steering operation.

• There are two types of four-wheel steering systems: active and passive.
• Passive systems use compliant rubber bushings, allowing a limited amount of rear wheel steering under load, which angles the rear wheels slightly toward the inside of the corner during turns and operated independently of the steering wheel and driver.
• In an active system, the rear wheels are usually steered using a computer and electric motors, but past systems have used mechanical connections between the front and rear steering boxes.
• Most active systems use a rack-and-pinion assembly driven by an electric motor, which turns the rear wheels when commanded by the steering control module.
• Most manufacturers have adopted the standard where at low speeds the rear wheels turn in the opposite direction to the front wheels to reduce turning radius, and at high speeds the rear wheels turn in the same direction as the front wheels to create smaller turning forces.
• Some manufacturers disable rear steering at high speeds and only allow rear steering at low speeds to allow tighter cornering.
• The parallelogram steering linkage is used where ride comfort is more important than sporty handling, such as in larger vehicles, and is more complicated than rack-and-pinion steering.

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 not a common steering system component?
   1. Steering column
   2. Steering knuckle
   3. Steering box
   4. Steering cylinder

2. Which part in the rack and pinion contains an inline ball and socket joint?
   1. The rack
   2. The inner tie rod
   3. The pinion
   4. The rubber bellows

3. Which part in the parallelogram steering linkage connects the pitman arm to the idler arm?
   1. The center link
   2. The tie rod end
   3. The steering damper
   4. The adjustment sleeve

4. Why is the steering intermediate shaft equipped with a flexible joint?
   1. To allow the angle of the wheels to change when they are steered
   2. To allow for drive by an electric motor on hybrid vehicles
   3. Because the steering column electric motor needs insulation
   4. Because the steering column sits at an angle to the box

5. What determines the turning rate on a rack and pinion?
   1. The tension on the guide yoke or rack bearing
   2. The gear ratio of the rack and pinion gears
   3. The length of the steering intermediate shaft
   4. The distance between the inner and outer tie rod

6. What is the purpose of the rolling balls on a recirculating ball steering box?
   1. To take up wear on the worm shaft
   2. To control the amount of play in the steering wheel
   3. To form a low-friction internal thread
   4. To stabilize the steering gear at high speeds

7. In a power steering system, which part controls the flow of fluid from side to side when the steering wheel is turned?
   1. The power steering pump rotor
   2. The power steering switch
   3. The power steering cooler
   4. The power steering rotary valve

8. In an electrically powered hydraulic steering (EPHS) system, where is the motor located?
   1. Connected to the power steering pump
   2. Connected to the rack and pinion assembly
   3. Connected to the steering column
   4. Connected to the steering intermediate shaft

9. In an electric power steering (EPS) system, what indicates steering wheel position and force to the ECU?
   1. The steering sensor
   2. The steering actuator
   3. The electric motor
   4. The EPS relay

10. In a passive four-wheel steering system, what allows the rear wheels to change angle around turns?
    1. The rear rack and pinion
    2. The rear steering actuator
    3. The compliant bushings
    4. The steering control module

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. Steering systems are being discussed. Technician A states that the steering knuckles typically pivot on ball joints. Technician B states that the steering arm converts rotary motion of the steering wheel to linear motion. Who is correct?
   1. Technician A
   2. Technician B
   3. Both A and B
   4. Neither A nor B

2. Steering geometry is being discussed. Technician A states that in a parallelogram steering system, the pitman arm and idler arm always move at right angles from one another. Technician B states that the steering arm transmits steering motion and force to the wheel assembly. Who is correct?
   1. Technician A
   2. Technician B
   3. Both A and B
   4. Neither A nor B

3. Parallelogram steering linkage is being discussed. Technician A states that the pitman arm connects the steering box to the center link. Technician B states that the idler arm is splined to the steering box. Who is correct?
   1. Technician A
   2. Technician B
   3. Both A and B
   4. Neither A nor B

4. Steering columns are being discussed. Technician A states that the steering column is equipped with a collapsible section to protect the driver in a collision. Technician B states that there may be various plastic shear pins and brackets which will break to allow extra movement in the case of a collision. Who is correct?
   1. Technician A
   2. Technician B
   3. Both A and B
   4. Neither A nor B

5. A high-mileage vehicle comes into the shop with excessive steering wheel play (looseness) when driving. The play is found to be inside of the steering rack and pinion assembly. Technician A states that the play is most likely caused by wear and backlash between the rack-and-pinion gears. Technician B states that most rack and pinions can be easily adjusted manually to make up for worn gears. Who is correct?
   1. Technician A
   2. Technician B
   3. Both A and B
   4. Neither A nor B

6. A worm steering gear box is being discussed. Technician A states that the steering gear box increases the driver’s force through large gear reduction. Technician B states that compared to a rack and pinion, the worm gear box isolates the driver much more effectively from road shock. Who is correct?
   1. Technician A
   2. Technician B
   3. Both A and B
   4. Neither A nor B

7. A vehicle with power steering is being discussed. Technician A states that a power steering reservoir is commonly mounted to the rack and pinion. Technician B states that the power steering pump is normally belt driven. Who is correct?
   1. Technician A
   2. Technician B
   3. Both A and B
   4. Neither A nor B

8. A vehicle with power steering is being discussed. Technician A states that a pressure switch or sensor will normally cause the engine rpm to stay steady or increase slightly when turning hard at low speeds. Technician B states that the torsion bar in the rack and pinion is used to control fluid flow, which provides steering assistance. Who is correct?
   1. Technician A
   2. Technician B
   3. Both A and B
   4. Neither A nor B

9. A vehicle with electronic power steering (EPS) comes into the shop. Technician A states that the system is designed with a failsafe so that it can still be steered in event of an electronic failure. Technician B states that the EPS system will likely be capable of some self-diagnosis and may set diagnostic trouble codes. Who is correct?
   1. Technician A
   2. Technician B
   3. Both A and B
   4. Neither A nor B

10. A vehicle with four-wheel steering is being discussed. Technician A states that most newer model vehicles can be special ordered with rear wheel steering as an option. Technician B states that most modern rear wheel steering racks are operated with hydraulics. 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.