After replacing the brake pads and rotors on a vehicle with drum rear brakes, the technician notices that the brake pedal feels lower than before, but there is no sponginess. The fluid level is full, and no leaks are present. What is the MOST likely cause?
- AA faulty master cylinder that failed during the service.
- BImproperly adjusted rear drum brakes.
- CAir in the hydraulic system from the front brake service.
- DOver-torqued lug nuts on the front wheels.
Show answer & explanationAnswer & explanation
Correct answer: B. Improperly adjusted rear drum brakes.
If the brake pedal feels lower but not spongy, and there are no leaks or air, it points to excessive travel needed to engage the brakes. In a system with drum rear brakes, if they are not properly adjusted (i.e., the shoes are too far from the drum), the master cylinder piston has to travel further to take up this slack before adequate pressure is built, resulting in a lower pedal. This is often overlooked when only front brakes are serviced if the rear drums were previously compensating for the worn front pads.
Why the other options are wrong
- A. A master cylinder failing during service is possible but less likely to be the *most* likely cause given the specific symptoms and recent front brake work, which doesn't directly affect the master cylinder's internal function.
- C. Air in the system causes a spongy pedal, not just a low pedal with a firm feel.
- D. Over-torqued lug nuts can cause rotor warpage or wheel bearing issues, but would not directly lead to a low brake pedal feel.
Drum Brake Adjustment and Pedal Height
The proper adjustment of drum brake shoes to maintain a minimal clearance with the drum is crucial for correct brake pedal height and feel.
- Excessive shoe-to-drum clearance causes a low brake pedal.
- Drum brakes often have self-adjusters that can fail or need manual adjustment after service.
- Proper adjustment ensures the master cylinder doesn't have to over-travel to build pressure.
Memory trick: Low and firm means the shoes are too far, not spongy air.