Automobile & Light Truck Certification Test A5 BrakesDisc Brake Diagnosis and RepairMedium
When inspecting a disc brake system, a technician observes a small amount of brake fluid weeping from around the caliper piston boot. The brake pedal feels firm, and there are no other apparent braking issues. What is the most appropriate action?
- AReplace the caliper, as the piston seal is compromised.
- BLubricate the piston boot to prevent further leakage.
- CTop off the master cylinder reservoir with brake fluid.
- DBleed the brake system to remove air.
Show answer & explanationAnswer & explanation
Correct answer: A. Replace the caliper, as the piston seal is compromised.
Any visible brake fluid leaking from around the piston boot indicates a compromised piston seal. The piston boot is only a dust seal; the primary hydraulic seal is behind it. A leaking primary seal means the caliper is failing and must be replaced or rebuilt to prevent future brake failure and fluid loss.
Why the other options are wrong
- B. Lubricating the piston boot is ineffective; the boot is a dust cover, not a hydraulic seal, and lubrication won't stop an internal leak.
- C. Topping off the reservoir only temporarily addresses fluid loss; it doesn't fix the underlying leak.
- D. Bleeding the system is for air removal, not for addressing a fluid leak from a seal.
Caliper Piston Leak
Brake fluid weeping from the caliper piston boot signifies a failed internal piston seal, requiring caliper replacement or rebuilding.
- Piston boot is a dust seal, not a fluid seal.
- Internal seal failure leads to fluid loss and potential brake failure.
- Caliper must be addressed immediately.
Memory trick: Fluid on the boot? The piston seal's kaput!