Automobile & Light Truck Certification Test A5 BrakesDrum Brake Diagnosis and RepairMedium
A technician is performing a pre-inspection of a drum brake assembly. They notice a small amount of brake fluid seeping from the boot of the wheel cylinder. The brake pedal feels slightly low but firm. Which of the following is the MOST appropriate action?
- ABleed the brake system and monitor for further leakage.
- BTighten the brake lines at the wheel cylinder and re-evaluate.
- CReplace the wheel cylinder and bleed the brake system.
- DAdd brake fluid to the master cylinder and adjust the parking brake.
Show answer & explanationAnswer & explanation
Correct answer: C. Replace the wheel cylinder and bleed the brake system.
Any visible seepage of brake fluid from a wheel cylinder boot indicates a failed internal seal. This is a critical safety concern as it will eventually lead to significant fluid loss and brake failure. Replacing the wheel cylinder and then bleeding the system is the only correct and safe repair. Monitoring or tightening will not fix a failed seal.
Why the other options are wrong
- A. Bleeding will temporarily remove air but won't fix the underlying leak, which will worsen.
- B. The leak is from the cylinder's internal seals, not the brake line connection, so tightening the line won't help.
- D. Adding fluid is a temporary measure and adjusting the parking brake does not address the wheel cylinder leak.
Wheel Cylinder Leak Diagnosis
Identifying the source and severity of brake fluid leakage from a wheel cylinder, typically indicated by fluid on the shoes or seeping from the dust boots.
- Fluid seepage from boot = failed internal seals.
- Leads to fluid loss, air entry, reduced braking.
- Requires replacement of the wheel cylinder, not just repair or monitoring.
Memory trick: Boot leak, fluid's out; replace the cylinder, no doubt!