Chassis, Steering, Suspension and Braking Systems
Chassis, Steering, Suspension and Braking Systems
This domain tests geometry, suspension and steering repair, hydraulic braking, ABS and electronic parking brakes. Expect questions on alignment angles, component checks, brake measurement and safe repair procedures.
Core rules
Check tyre pressures and wear before alignment. Four-wheel alignment uses camber, caster, toe, thrust angle and steering-axis inclination. Correct rear thrust angle before adjusting front toe, and centre the steering wheel. Torque suspension bushes at ride height so they are not pre-twisted. Check ball joints and track rod ends for play under load. Brake diagnosis includes disc thickness, thickness variation, runout, pad condition and fluid condition. A pulsating pedal often indicates disc thickness variation or runout, not just warped discs. Use the electronic parking brake service mode before retracting calipers.
Worked example
A vehicle pulls right. Reasoning: check pressures and tyre condition first; road test to confirm; then measure alignment. If rear thrust is out and front toe is out, correct rear toe first, then front toe, and recheck. If caster differs by more than about 0.5 degrees side to side, inspect for a bent strut, control arm or subframe. Do not simply adjust toe to hide a pull.
Traps
- Adjusting toe with worn track rod ends.
- Failing to centre the steering wheel after alignment.
- Forcing an electronic parking brake piston without service mode.
- Torquing suspension bushes at full droop.
- Ignoring tyre pressures before geometry work.