Braking, Steering and Suspension Systems
This domain examines vehicle control, ride and safety. Questions cover hydraulic braking principles, brake bleeding and component inspection, steering geometry, power steering, suspension types and tyre wear diagnosis.
Braking and steering
- Hydraulic braking follows Pascal's law: pressure applied to a confined fluid is transmitted equally in all directions. A larger caliper piston area produces greater clamping force but more pedal travel.
- Brake fluid is hygroscopic. Use the specified DOT grade; never mix DOT 5 silicone with DOT 3 or 4 glycol fluid. Bleed in the specified sequence to remove air.
- Disc brakes resist fade better; drum brakes use a wheel cylinder and return springs. ABS prevents wheel lock-up but does not guarantee a shorter stop on loose gravel.
- Steering geometry includes camber (vertical tilt), caster (steering-axis tilt) and toe (front-to-rear difference). Incorrect toe quickly wears tyres.
Suspension
- Springs support weight; shock absorbers control oscillation. A MacPherson strut combines spring, damper and location. Worn ball joints, bushes or wheel bearings cause clunks, play and uneven tyre wear.
Worked example
A driver applies 200 N to a brake pedal with a 4:1 pedal ratio. The master cylinder piston area is 2 cm² and one caliper piston area is 16 cm². Reasoning: force at master cylinder = 200 × 4 = 800 N. Pressure = 800 ÷ 2 = 400 N/cm². Caliper force = 400 × 16 = 6400 N. This shows how hydraulic area multiplies force.
Traps
Confusing camber with caster, adjusting toe before camber and caster, mixing brake fluid grades, and checking tyre pressure when hot are frequent errors. Never reuse contaminated brake fluid or leave a brake hose twisted.