Automobile & Light Truck Certification Test A5 BrakesDisc Brake Diagnosis and RepairHard
A technician is installing new brake pads and rotors on a vehicle. After installation, they notice that the new pads are making light contact with the rotor even when the brake pedal is not applied, causing a slight drag. All components are new and installed correctly. Which of the following is the MOST likely cause?
- AAn improperly adjusted parking brake.
- BA collapsed brake hose.
- CInsufficient master cylinder fluid level.
- DA residual pressure valve in the disc brake circuit.
Show answer & explanationAnswer & explanation
Correct answer: B. A collapsed brake hose.
A collapsed or internally swollen brake hose can act as a one-way valve, allowing fluid to pass to the caliper under pressure but preventing it from returning fully to the master cylinder when the pedal is released. This traps pressure in the caliper, causing the pads to drag. Since all components are new and installed correctly, and the parking brake is separate, a collapsed hose is the most probable cause.
Why the other options are wrong
- A. An improperly adjusted parking brake would cause drag in the rear (if drum or hat-type) but wouldn't typically affect new disc brake pads dragging on their own unless it's a caliper-actuated system and adjusted too tight.
- C. Insufficient fluid level would cause a low or spongy pedal and reduced braking, not constant pad drag.
- D. Residual pressure valves are used in drum brake systems to maintain slight pressure against the shoes, but are generally not used in disc brake circuits as they would cause constant pad drag.
Brake Hose Restriction
An internal collapse or blockage within a brake hose that restricts fluid flow, often preventing brake fluid from returning from the caliper to the master cylinder, leading to dragging brakes.
- Acts like a one-way valve.
- Causes pads to drag, overheating, and reduced fuel economy.
- Requires hose replacement.
Memory trick: Drag means friction, check the fluid path, then component action.