Automobile & Light Truck Certification Test A5 BrakesDrum Brake Diagnosis and RepairEasy
A technician is performing a rear drum brake service. After replacing the shoes and inspecting the wheel cylinders, they find that the automatic adjusters are rusted and seized. What is the MOST critical reason to replace these adjusters?
- AThey will cause the brake pedal to feel too firm.
- BThey will cause excessive brake dust accumulation.
- CThey will lead to premature wear of the parking brake cable.
- DThey will prevent the shoes from maintaining correct drum clearance.
Show answer & explanationAnswer & explanation
Correct answer: D. They will prevent the shoes from maintaining correct drum clearance.
The primary function of automatic adjusters in drum brakes is to maintain the correct clearance between the brake shoes and the drum as the lining wears. If they are seized, this clearance will become excessive, leading to a low brake pedal, increased pedal travel, and reduced braking efficiency. It is critical for safety and performance.
Why the other options are wrong
- A. A firm pedal is usually associated with a lack of power assist or air in the hydraulic system, not seized adjusters, which would cause a lower, longer pedal.
- B. Seized adjusters do not directly cause excessive brake dust; that is more related to lining material or hard braking.
- C. While parking brake adjustment is related, seized adjusters primarily affect service brake clearance, not cable wear.
Automatic Brake Adjuster
A mechanism in drum brake systems that automatically compensates for brake shoe lining wear by adjusting the shoe-to-drum clearance to maintain consistent pedal height and braking performance.
- Operates during reverse braking or parking brake application.
- Prevents excessive pedal travel as shoes wear.
- Malfunction leads to low pedal, reduced braking efficiency.
Memory trick: Adjusters keep the gap just right, for a pedal that feels tight.