CDL General Knowledge TestAir Brakes (if applicable)Medium
A driver is inspecting the brake drums on an air brake equipped vehicle. Which of the following conditions indicates a problem that requires immediate attention?
- AThe drum surface is slightly discolored from heat.
- BThe drum is worn smoothly with no deep grooves.
- CThe drum has cracks longer than 1/2 inch.
- DThere is a thin, even layer of brake dust inside the drum.
Show answer & explanationAnswer & explanation
Correct answer: C. The drum has cracks longer than 1/2 inch.
Cracks in a brake drum, especially those longer than 1/2 inch, indicate structural weakness and a high risk of drum failure, which could lead to complete brake loss. This requires immediate attention and replacement.
Why the other options are wrong
- A. Slight discoloration from heat is common and generally not an immediate safety concern unless accompanied by other severe symptoms.
- B. A smoothly worn drum with no deep grooves is a sign of normal wear and good condition, not a problem.
- D. A thin, even layer of brake dust is normal and expected; excessive or uneven dust might indicate other issues but not directly a drum problem.
Brake Drum Inspection
Visual examination of the brake drums for defects, wear, and damage that could impair braking performance.
- Look for cracks, heat spots, and excessive wear.
- Cracks over 1/2 inch are critical defects.
- Essential part of pre-trip and post-trip inspections.
Memory trick: Drum's Got Cracks? Time for New Tracks!