Braking Systems
Braking concepts
Know how hydraulic pressure transmits force, why pedal ratio and bore size affect feel, and how master cylinders, proportioning valves, ABS hydraulic units, calipers, pads, discs, drums and parking brakes work together. Understand brake fluid hygroscopic behaviour, boiling point, bleeding and contamination. ABS and stability control need wheel-speed signals, yaw and pressure sensors; a warning lamp may disable both. Servicing includes disc thickness and runout, pad wear, caliper slide condition, hose condition, drum adjustment and correct torque.
Traps
Spongy pedal usually indicates air or a hydraulic leak; a pedal that slowly sinks under steady pressure suggests an internal master-cylinder leak. Fade after repeated hard stops is heat-related, not air. A pull under braking can come from a seized caliper, collapsed hose, contaminated pad or uneven tyre pressure, so do not assume alignment. Never push contaminated fluid back through an ABS unit, and follow the maker’s sequence for bleeding and electronic parking-brake retraction. Mixing DOT grades or using mineral oil in a glycol system can destroy seals.
Worked example
For a low, sinking pedal: check fluid level and external leaks, pressure-bleed if specified, then isolate the master cylinder with plugs. If the pedal still sinks with the outlet blocked, the master cylinder is suspect. Rule of thumb: brake faults are hydraulic, mechanical or electronic; test the hydraulic circuit before replacing ABS components.
Exam approach
Prioritise safety: any fluid leak, damaged hose or inconsistent pedal means the vehicle should not road-test until repaired.