CDL General Knowledge TestAir Brakes (if applicable)Easy
A driver is performing a final air brake check before starting a trip. They engage the parking brake and then release it, noting that the parking brake knob pops out. What does this indicate?
- AThere is a significant leak in the gladhand connections.
- BThe parking brake system is operating as designed.
- CThe air compressor is malfunctioning.
- DThe service brakes are fully engaged.
Show answer & explanationAnswer & explanation
Correct answer: B. The parking brake system is operating as designed.
The parking brake knob on an air brake system is designed to pop out when the parking brakes are engaged (set) and be pushed in to release them. This action confirms the parking brake system is functioning correctly.
Why the other options are wrong
- A. Gladhand leaks would cause air pressure loss, but the knob's action itself is about engagement, not necessarily the presence of a leak at that specific moment.
- C. The parking brake popping out is a normal function and does not indicate a compressor malfunction.
- D. The parking brake operates independently of the service brakes, though both use air.
Parking Brake Knob Function
The control that engages and releases the spring parking brakes in an air brake system.
- Pops out to engage (set) parking brake.
- Pushed in to release parking brake.
- Indicates air pressure is either removed from or supplied to the spring brakes.
Memory trick: Knob out, brakes are stout.