Automobile & Light Truck Certification Test A5 BrakesDisc Brake Diagnosis and RepairHard
A customer reports a squealing noise from the front brakes only when the brakes are NOT applied. The noise stops as soon as the brake pedal is lightly pressed. Which of the following is the most probable cause?
- AWorn brake pads with activated wear indicators.
- BAir trapped in the brake lines.
- CA warped brake rotor causing intermittent contact.
- DImproperly installed or missing anti-rattle clips.
Show answer & explanationAnswer & explanation
Correct answer: D. Improperly installed or missing anti-rattle clips.
A squealing noise when brakes are NOT applied, which stops upon light application, is a classic symptom of brake pad vibration or movement within the caliper. This is often caused by improperly installed or missing anti-rattle clips (also known as pad shims or hardware) that are designed to hold the pads snugly in place.
Why the other options are wrong
- A. Worn brake pad indicators typically make noise *when* the brakes are applied, alerting the driver to low pad material.
- B. Air trapped in the brake lines would result in a spongy pedal and reduced braking effectiveness, not a specific squealing noise when brakes are off.
- C. A warped brake rotor would typically cause pulsation and noise *during* braking, not when the brakes are off.
Brake Squeal (Brakes Off)
A squealing noise when brakes are not applied, which stops with light pedal pressure, is typically caused by loose brake pads vibrating, often due to faulty anti-rattle clips.
- Indicates loose pad fitment in the caliper bracket.
- Anti-rattle clips (hardware) are crucial for pad stability.
- Noise stops when pads are held firm by light pressure.
Memory trick: Squeal when idle? Anti-rattle clips are vital!