Automobile & Light Truck Certification Test A5 BrakesDisc Brake Diagnosis and RepairEasy
A technician is inspecting a vehicle with a complaint of a squealing noise from the front brakes only when the brakes are applied. The noise is consistent and high-pitched. Which of the following is the MOST likely cause?
- AA faulty steering rack.
- BGlazed brake pads or rotors.
- CA loose lug nut.
- DWorn wheel bearings.
Show answer & explanationAnswer & explanation
Correct answer: B. Glazed brake pads or rotors.
A high-pitched squeal during braking is most commonly caused by brake pad vibration against the rotor, often due to glazed friction material on the pads or a hard, smooth surface on the rotor. It can also be caused by wear indicators, but glazed components are a very common source.
Why the other options are wrong
- A. A faulty steering rack would affect steering feel and control, not directly cause a brake squeal.
- C. A loose lug nut would cause a clunking or thumping noise, especially during cornering or acceleration, not a squeal during braking.
- D. Worn wheel bearings typically cause a humming or growling noise, not a high-pitched squeal during braking.
Brake Squeal Causes
Common reasons for a high-pitched noise during brake application.
- Pad wear indicators.
- Glazed pads or rotors.
- Improper lubrication of pad backing plates/caliper contact points.
- Pad vibration due to poor fitment or missing anti-rattle hardware.
Memory trick: Squeaky brakes, check for mistakes.