Braking, Steering and Suspension Systems
Braking, Steering and Suspension Systems
This domain tests hydraulic braking, ABS, steering geometry and suspension construction, with emphasis on fault symptoms and safe repair. Expect master cylinder, bleeding, disc and drum brakes, wheel alignment angles, power steering and shock absorbers.
Core rules and concepts
- Pascal's law says pressure transmits equally in a confined fluid. Brake force depends on pressure and piston area.
- Brake fluid is hygroscopic. DOT 3 and DOT 4 are glycol based; DOT 5 is silicone based. Never mix them, and flush to the specified schedule.
- Bleed brakes in the specified order, usually starting farthest from the master cylinder, keeping the reservoir full. A spongy pedal means air; a pedal that sinks under steady pressure means a leak or master-cylinder bypass.
- Disc brakes need pad, thickness and runout checks. Drum brakes need shoe adjustment and wheel-cylinder leak checks.
- ABS uses wheel-speed sensors and a hydraulic modulator. Keep sensors and rings clean; do not measure resistance on a live circuit.
- Steering angles include camber, caster, toe and steering-axis inclination. Toe is adjusted at the tie rods with the steering centred.
- Springs support load; shock absorbers damp movement. Check ball joints, bushes and strut mounts.
Worked example
After a brake repair the pedal is spongy and slowly sinks. Reasoning: spongy feel points to air, while sinking points to fluid loss or master-cylinder bypass. Pressure-bleed in the correct order, check all joints for leaks, then hold steady pedal pressure. If it still sinks, isolate the master cylinder with approved plugs and inspect it.
Traps that cost marks
Pressing the brake pedal with a caliper removed; mixing DOT fluids; adjusting toe with the steering wheel off centre; reusing stretch suspension bolts; and skipping steering-angle sensor calibration after alignment.
Key points
- Spongy pedal means air; sinking pedal means leak or bypass.
- Never mix glycol and silicone brake fluids.
- Bleed farthest wheel first and keep the reservoir full.
- Toe is set with the steering centred.
- Recalibrate driver-assistance sensors after alignment.