Automobile & Light Truck Certification Test A5 BrakesDrum Brake Diagnosis and RepairMedium
A customer complains that their vehicle pulls to the left when the brakes are applied. During inspection, the right rear drum brake assembly is found to have a greasy, fluid-soaked brake shoe. The left rear brake appears normal. What is the MOST likely cause of the pull?
- AAn improperly adjusted parking brake on the right rear.
- BA seized automatic adjuster on the left rear.
- CA faulty right rear wheel cylinder seal.
- DA collapsed brake hose leading to the left front caliper.
Show answer & explanationAnswer & explanation
Correct answer: C. A faulty right rear wheel cylinder seal.
Greasy, fluid-soaked brake shoes indicate a leak, most commonly from a failed wheel cylinder seal or a leaking axle seal. When brake fluid or axle grease contaminates a brake shoe, it drastically reduces its friction coefficient, causing that wheel's brake to lose effectiveness. If the right rear brake is ineffective due to contamination, the left rear brake will apply normally, causing the vehicle to pull to the left.
Why the other options are wrong
- A. An improperly adjusted parking brake might cause drag, but typically wouldn't cause a pull unless it's severely seized on one side and not the other, and it wouldn't cause a greasy shoe.
- B. A seized adjuster on the left rear would cause that brake to be less effective, leading to a pull to the right, not the left.
- D. A collapsed left front brake hose would cause a pull to the right (due to reduced left front braking), and the problem is described in the rear drum brake system.
Brake Shoe Contamination
The presence of oil, grease, or brake fluid on the friction material of a brake shoe, significantly reducing its coefficient of friction and braking effectiveness.
- Causes: leaking wheel cylinder, leaking axle seal, improper lubrication.
- Symptoms: reduced braking efficiency, pulling to one side, spongy pedal if fluid leak is severe.
- Remedy: replace contaminated shoes and repair the source of the leak.
Memory trick: Grease on a shoe means less grip, so the car will pull to the other hip.