Automobile & Light Truck Certification Test A5 BrakesDrum Brake Diagnosis and RepairMedium
A technician is performing a pre-inspection of a drum brake system. They notice a significant amount of black, greasy residue on the inside of the brake drum and on the brake shoes. The drum itself appears to be slightly scored. What is the MOST likely source of this contamination?
- AAn axle seal leak.
- BA leaking wheel cylinder.
- CWorn-out brake shoes.
- DA faulty automatic adjuster.
Show answer & explanationAnswer & explanation
Correct answer: A. An axle seal leak.
Black, greasy residue on the inside of the brake drum and shoes is a strong indicator of an axle seal leak. Gear oil from the differential can seep past a faulty axle seal and contaminate the drum brake components, leading to reduced braking effectiveness and potential scoring.
Why the other options are wrong
- B. A leaking wheel cylinder would typically result in brake fluid (amber or clear) contamination, not black greasy residue.
- C. Worn-out brake shoes would produce brake dust (dark, powdery) and potentially cause scoring, but not greasy residue.
- D. A faulty automatic adjuster would cause poor adjustment and excessive pedal travel, not greasy contamination.
Axle Seal Leak Symptoms
An axle seal leak in a drum brake system results in black, greasy contamination on the brake shoes and drum, leading to reduced braking and potential scoring.
- Black, greasy residue
- Contaminates brake shoes
- Reduces braking effectiveness
Memory trick: Fluid is clear, oil is black, dust is just a powdery attack.