CDL Air Brakes TestAir Brake System PartsMedium
A driver is operating a commercial vehicle and notices that the service brakes feel 'spongy' and require greater pedal effort to achieve effective braking. During a visual inspection, they see no obvious air leaks. Which component is most likely contributing to this 'spongy' brake feel?
- AA stuck open safety valve on an air tank.
- BA malfunctioning alcohol evaporator.
- CA faulty air compressor governor.
- DWorn foundation brakes (e.g., brake linings or drums).
Show answer & explanationAnswer & explanation
Correct answer: D. Worn foundation brakes (e.g., brake linings or drums).
A spongy brake pedal feel, especially requiring greater effort for braking, often indicates issues with the foundation brakes. Worn brake linings, drums, or slack adjusters can lead to excessive travel in the brake components, requiring more air pressure and pedal travel to achieve effective braking.
Why the other options are wrong
- A. A stuck open safety valve would cause a continuous air leak and loss of system pressure, not typically a 'spongy' feel at full pressure.
- B. An alcohol evaporator prevents freezing; it doesn't impact brake pedal feel.
- C. A faulty governor affects air pressure build-up and cut-out, not directly the 'feel' of the service brakes.
Foundation Brakes Wear
Wear in components like brake linings, drums, or slack adjusters in the foundation brakes can lead to reduced braking effectiveness and a 'spongy' feeling in the brake pedal.
- Includes brake shoes, drums, slack adjusters, brake chambers.
- Wear increases required pedal effort/travel.
- Causes reduced braking efficiency.
Memory trick: Worn parts make the pedal Weak, requiring more work.