Automobile & Light Truck Certification Test A5 BrakesDrum Brake Diagnosis and RepairMedium
A customer reports that their vehicle's rear brakes make a loud grinding noise when applied. Upon inspection, a technician finds deep scoring marks on the inside surface of the brake drum. What is the most probable cause of this condition?
- AA misadjusted parking brake cable
- BInsufficient brake fluid in the reservoir
- CWorn-out brake shoes with exposed rivets or metal backing
- DA seized wheel cylinder
Show answer & explanationAnswer & explanation
Correct answer: C. Worn-out brake shoes with exposed rivets or metal backing
Deep scoring marks on a brake drum, accompanied by a grinding noise, are a strong indicator that the friction material of the brake shoes has worn away completely, allowing the metal backing plate or rivets to contact and abrade the drum.
Why the other options are wrong
- A. A misadjusted parking brake cable would cause the brake to drag or not engage, without necessarily scoring the drum.
- B. Insufficient brake fluid affects hydraulic pressure and pedal feel, not direct mechanical wear on the drum surface.
- D. A seized wheel cylinder would cause uneven braking or a dragging brake, not direct drum scoring.
Brake Drum Scoring
Brake drum scoring refers to deep grooves or gouges on the drum's friction surface, typically caused by metal-to-metal contact due to worn-out brake shoes.
- Caused by worn brake shoes exposing metal components.
- Results in a loud grinding noise during braking.
- Requires drum resurfacing or replacement, and new shoes.
Memory trick: Metal on Metal Makes a Grinding Sound