ASE G1 Auto Maintenance and Light RepairBrakesMedium
A customer complains of a high-pitched squealing noise coming from the front brakes during light application. The sound disappears when the brakes are applied firmly. A technician inspects the brakes and finds the pads have approximately 50% lining remaining and the rotors are in good condition. What is the MOST likely cause of this noise?
- AWorn wheel bearings.
- BGlazed brake pads or rotors.
- CBrake pad wear indicators contacting the rotor.
- DImproperly lubricated caliper guide pins.
Show answer & explanationAnswer & explanation
Correct answer: B. Glazed brake pads or rotors.
A high-pitched squeal during light braking that disappears under firm application is a classic symptom of glazed brake pads or rotors. Glazing occurs when excessive heat causes the friction material to harden, reducing its effectiveness and leading to noise.
Why the other options are wrong
- A. Worn wheel bearings typically produce a growling or humming noise that changes with vehicle speed or turning, not a high-pitched squeal during braking.
- C. Brake pad wear indicators produce a consistent, often metallic, squealing or scraping sound when the pads are worn to their minimum thickness, which is not the case with 50% lining remaining.
- D. Improperly lubricated caliper guide pins can cause uneven pad wear, pulling, or a clunking noise, but not typically a high-pitched squeal during light braking.
Brake Glazing
Brake glazing is the hardening of brake pad friction material or rotor surface due to excessive heat, leading to reduced braking effectiveness and a high-pitched squealing noise.
- Caused by heat
- Reduces friction
- Squealing noise common
Memory trick: Squeal light, quiet firm, a glazed surface you'll affirm.