Service and Repair Chassis, Suspension, Steering, and Brake Systems
What this domain tests
This domain covers inspection and repair of suspension, steering, wheel alignment, and brakes, including ABS. Expect questions on tire wear patterns, joint play, alignment angles, brake hydraulics, and bleeding.
Core rules and concepts
- Inspect tires for wear patterns: both outer edges worn suggests underinflation; one outer edge suggests camber; feathered tread suggests toe.
- Check ball joints, tie-rod ends, wheel bearings, and bushings for play with the suspension loaded as specified.
- Alignment angles: camber is vertical tilt, caster is steering-axis tilt, and toe is the difference in front and rear of the tires. Set toe after camber and caster.
- Brake service includes measuring pad thickness, rotor thickness, and rotor runout. Do not machine below the minimum thickness.
- Brake fluid is hygroscopic; use the specified DOT rating and bleed in the manufacturer's sequence, often right rear, left rear, right front, left front.
Worked example
A vehicle has a spongy brake pedal. The technician checks for leaks, then bleeds the system. Air in the hydraulic circuit compresses, so pedal travel increases. After bleeding and confirming a firm pedal, the repair is road-tested. The reasoning is that hydraulics transmit force; trapped air weakens that transmission.
Traps that cost marks
Pushing caliper pistons back without opening the bleeder; mixing DOT 3 and DOT 5 fluid; tightening suspension bolts with the vehicle hanging; and skipping ABS bleed procedures after air enters the modulator.
Key points
- Tire wear patterns indicate alignment or pressure faults.
- Set camber and caster before toe.
- Measure rotor thickness and runout.
- Use the specified brake fluid and bleed sequence.
- Road-test brake and steering repairs.