CDL Air Brakes TestAir Brake System PartsMedium
A commercial vehicle driver is performing a pre-trip inspection. After charging the system to full pressure, they turn off the engine and observe a continuous, audible air leak coming from the area of the brake pedal. What does this most likely indicate?
- AA malfunctioning foot brake (treadle) valve.
- BA faulty air compressor governor.
- CA leaking service brake chamber.
- DA cracked air storage tank.
Show answer & explanationAnswer & explanation
Correct answer: A. A malfunctioning foot brake (treadle) valve.
A continuous air leak from the area of the brake pedal after the engine is off and the system is charged often points to an internal leak within the foot brake (treadle) valve. This valve controls the air flow to the service brakes and can develop internal leaks.
Why the other options are wrong
- B. A faulty governor would affect compressor cycling, not a continuous leak from the pedal area with the engine off.
- C. A leaking brake chamber would be located at the wheel end and would likely cause the compressor to cycle more frequently, but not a continuous leak at the pedal.
- D. A cracked air storage tank would result in a leak from the tank itself, not specifically from the brake pedal area.
Foot Brake Valve Leak
An internal or external air leak originating from the foot brake (treadle) valve, often heard as a continuous hiss from the pedal area, even when brakes are not applied.
- Can lead to loss of air pressure over time.
- Indicates a faulty or worn foot valve.
- Requires replacement or repair of the valve.
- Can affect service brake performance.
Memory trick: Pedal hisses, air escapes, the foot valve has some leaky scrapes.