Automobile & Light Truck Certification Test A5 BrakesDisc Brake Diagnosis and RepairMedium
While replacing brake pads, a technician attempts to compress a single-piston caliper piston using a C-clamp, but it resists compression significantly. After opening the bleeder screw, the piston compresses easily. What does this indicate?
- AAn internally restricted brake hose.
- BA faulty master cylinder.
- CExcessive residual pressure in the brake system.
- DA seized caliper piston.
Show answer & explanationAnswer & explanation
Correct answer: A. An internally restricted brake hose.
If the piston is hard to compress with the bleeder closed but easy with it open, it means there's hydraulic pressure trapped in the caliper that can't return to the master cylinder. This is a classic symptom of an internally restricted brake hose, which acts like a one-way valve, allowing fluid to flow in but not out.
Why the other options are wrong
- B. A faulty master cylinder might cause a soft pedal or general brake drag, but not this specific symptom of pressure relief through the bleeder.
- C. While there is excessive pressure, the root cause is the restriction preventing its release, not just a general 'excessive residual pressure' (which is normal to some extent).
- D. A seized piston would resist compression even with the bleeder screw open.
Brake Hose Restriction
An internal collapse or blockage within a flexible brake hose, typically acting as a check valve.
- Allows fluid to flow to the caliper, but restricts return.
- Causes brake drag and potential overheating.
- Diagnosed by opening bleeder to relieve pressure.
Memory trick: Hard push, easy bleed, hose in need.