Braking Systems and Hydraulics
Braking Systems and Hydraulics
This domain tests hydraulic principles, component inspection, bleeding, and brake performance. The exam expects safe work habits and measurement, not guesswork.
Core rules
- Brake fluid is hygroscopic. Use the specified DOT fluid, keep containers sealed, and do not mix DOT 5 silicone with DOT 3 or 4 systems.
- Measure pad thickness and rotor thickness with a micrometer; compare with the minimum marked on the rotor or in the manual. Check runout and parallelism when diagnosing pulsation.
- A spongy pedal indicates air or a flexible-line fault. A low pedal can indicate rear brake adjustment, a failed master cylinder, or a leak. A hard pedal can indicate a booster fault.
- Bleed in the sequence specified by the manufacturer; many systems require longest-to-shortest, and ABS units may need a scan tool to cycle valves.
Worked example
After pad replacement, the pedal is spongy and sinks slowly at a stop. First check for leaks and fluid level. If the pedal pumps up, air is likely in the system. Pressure-bleed or manually bleed in the correct sequence, keeping the reservoir above the minimum. If the pedal still sinks with steady pressure and no external leak, suspect an internal master-cylinder bypass. Do not replace the ABS unit before this test.
Traps
Pushing caliper pistons back without opening the reservoir or checking for ABS backflow, twisting a brake hose, using mineral oil near brake seals, and fitting pads without cleaning and lubricating the correct contact points.