Automobile & Light Truck Certification Test A5 BrakesDrum Brake Diagnosis and RepairMedium
A customer complains that their vehicle's rear brakes make a loud grinding noise when applied. Upon inspection, the technician finds that the brake drum has deep, concentric grooves and metallic particles embedded in the drum surface. What is the MOST likely cause of this condition?
- AGlazed brake shoes
- BA faulty wheel cylinder
- CContaminated brake fluid
- DWorn-out brake shoes with exposed rivets/metal
Show answer & explanationAnswer & explanation
Correct answer: D. Worn-out brake shoes with exposed rivets/metal
Deep concentric grooves and metallic particles embedded in the drum surface, accompanied by a grinding noise, are classic symptoms of brake shoes that have worn past their friction material, exposing the metal backing plate or rivets. This metal-on-metal contact severely damages the drum.
Why the other options are wrong
- A. Glazed shoes cause reduced braking and sometimes squealing, not deep grinding and drum damage.
- B. A faulty wheel cylinder would typically cause leaks, soft pedal, or uneven braking, not direct grinding and drum damage.
- C. Contaminated brake fluid affects hydraulic function, not direct mechanical wear on the drum surface.
Brake Drum Scoring Cause
Deep grooves or damage to the brake drum's friction surface, often caused by metal-on-metal contact from worn-out brake shoes.
- Results in loud grinding noises
- Indicates severely worn brake shoes
- Requires drum replacement or machining, and new shoes
Memory trick: Grind and groove, metal's the proof.