Automobile & Light Truck Certification Test A5 BrakesHydraulic System Diagnosis and RepairMedium
A technician is inspecting a vehicle that has recently had new brake pads and rotors installed. The customer complains that the brake pedal feels 'low' and requires excessive travel before the brakes engage, but braking performance is otherwise good. Which of the following is the MOST likely cause?
- AA collapsed flexible brake hose
- BAir trapped in the hydraulic system
- CA faulty master cylinder check valve
- DImproperly adjusted rear drum brakes
Show answer & explanationAnswer & explanation
Correct answer: D. Improperly adjusted rear drum brakes
A low pedal after brake work, especially if pads and rotors were replaced, often points to an issue with rear drum brake adjustment. If the shoes are too far from the drums, the pedal will travel excessively before contact, even if there are no hydraulic issues.
Why the other options are wrong
- A. A collapsed flexible brake hose would typically cause a drag or pull to one side, not just a low pedal.
- B. Air in the system would cause a spongy pedal that might firm up with pumping, not just a low pedal with good performance.
- C. A faulty master cylinder check valve (residual pressure valve) would typically cause a hard pedal or no pressure, or a spongy pedal if it's allowing air in, not just a low pedal with good performance.
Drum Brake Adjustment
The process of setting the brake shoes' distance from the drum, crucial for proper pedal height and effective braking in drum brake systems.
- Manual or automatic adjusters.
- Incorrect adjustment leads to low pedal or excessive travel.
- Must be checked after brake service or often during inspection.
Memory trick: Low pedal woes, check drum shoes.