Braking Systems
Core concepts
Understand hydraulic principles (Pascal's law), master cylinder operation, proportioning valves, and the difference between disc and drum brakes. Know how antilock braking systems (ABS) use wheel speed sensors and hydraulic control units, and how electronic stability control builds on ABS. Be able to explain brake fade, pedal feel, and the purpose of a residual pressure valve in some systems.
Traps to expect
Questions often confuse a low pedal caused by air in the system with one caused by a leaking wheel cylinder or a faulty master cylinder. A spongy pedal usually indicates air; a pedal that slowly sinks under steady pressure suggests an internal master cylinder leak. Another trap is ABS: a wheel speed sensor fault can disable ABS and illuminate the light, but it does not mean the base brakes failed. Also remember that brake fluid is hygroscopic and should be tested for moisture.
Worked example
A pedal sinks slowly while held. Rule of thumb: if the pedal holds firm with the engine off but sinks when running, suspect a booster or check valve; if it sinks in both cases, suspect the master cylinder. Confirm by capping the master cylinder ports and rechecking.
Study strategy
Trace hydraulic pressure from master cylinder to caliper, practice bleeding sequence, and explain how ABS modulates pressure during a skid.