Automobile & Light Truck Certification Test A5 BrakesDrum Brake Diagnosis and RepairEasy
A technician is inspecting a drum brake system. Upon removal of the drum, they notice significant scoring and heat checking on the drum's friction surface. Which of the following is the MOST appropriate next step?
- AReplace the brake shoes and reassemble the system.
- BApply a thin layer of grease to the drum surface to reduce noise.
- CResurface the drum if it is within its maximum diameter specification.
- DAdjust the parking brake cable tension to compensate for the scoring.
Show answer & explanationAnswer & explanation
Correct answer: C. Resurface the drum if it is within its maximum diameter specification.
Significant scoring and heat checking indicate damage to the drum's friction surface. If the drum is still within its maximum allowable diameter after machining, resurfacing (turning) can restore a smooth surface for proper brake shoe contact. If it's beyond the specification, replacement is necessary.
Why the other options are wrong
- A. Replacing shoes without addressing the damaged drum will lead to premature wear of the new shoes and poor braking performance.
- B. Applying grease to a drum's friction surface is extremely dangerous as it will cause brake failure.
- D. Adjusting the parking brake will not address the drum's damage and will not improve service brake performance.
Brake Drum Inspection
The process of visually and dimensionally checking a brake drum for wear, damage, and specified limits to ensure safe and effective braking.
- Check for scoring, cracks, and heat checking.
- Measure drum diameter for wear and runout.
- Compare measurements to manufacturer specifications for maximum diameter.
Memory trick: See the damage, measure the limit, then fix or ditch it.