Automobile & Light Truck Certification Test A5 BrakesDisc Brake Diagnosis and RepairMedium
A vehicle owner complains of a burning smell and reduced braking performance after a short drive. Upon inspection, one of the rear wheels is significantly hotter than the others, and the disc rotor shows signs of discoloration. Which of the following is the most probable cause?
- AAn underfilled master cylinder reservoir.
- BA stuck or dragging parking brake cable.
- CA faulty wheel speed sensor.
- DAir in the brake line.
Show answer & explanationAnswer & explanation
Correct answer: B. A stuck or dragging parking brake cable.
A burning smell, reduced braking, and an excessively hot, discolored rotor on a single wheel are classic symptoms of a dragging brake. A stuck or dragging parking brake cable, especially on a rear wheel, would keep the brake partially applied, generating excessive heat and wear.
Why the other options are wrong
- A. An underfilled master cylinder reservoir would lead to a low pedal and reduced braking for the entire system or a circuit, not localized dragging.
- C. A faulty wheel speed sensor would primarily affect ABS operation and could cause an ABS warning light, but not directly a dragging brake.
- D. Air in the brake line would cause a spongy pedal and reduced braking on the affected circuit, not typically localized overheating on one wheel.
Dragging Brake Symptoms
Symptoms of a dragging brake include burning smell, reduced performance, excessive heat, and rotor discoloration, often due to mechanical binding.
- Caused by caliper not releasing, or parking brake issues.
- Leads to premature wear and potential brake failure.
- Can be identified by abnormal wheel temperature.
Memory trick: Hot wheel, burning smell? Parking brake cable's not doing well!