CDL Air Brakes TestInspecting Air Brake SystemsMedium
A driver is performing a functional check of the parking brake on a tractor-trailer. After building full air pressure, setting the parking brake, and putting the vehicle in a low gear, the driver gently pulls against the brake. The vehicle should:
- ARoll freely, indicating a complete failure of the parking brake system.
- BHold firmly, confirming the parking brake is fully engaged and effective.
- CMove slightly before stopping, indicating a functional but weak parking brake.
- DEngage the service brakes automatically, preventing movement.
Show answer & explanationAnswer & explanation
Correct answer: B. Hold firmly, confirming the parking brake is fully engaged and effective.
The parking brake test is designed to confirm that the spring brakes are strong enough to hold the vehicle. When the parking brake is set and the driver gently pulls in a low gear, the vehicle should not move at all, indicating the parking brake is holding firmly and is effective.
Why the other options are wrong
- A. Rolling freely means the parking brake has failed completely, making the vehicle unsafe to operate.
- C. Slight movement indicates a weak or failing parking brake, which is unsafe.
- D. The service brakes are not automatically engaged during a parking brake test; only the spring brakes (parking brake) should hold the vehicle.
Parking Brake Test
A pre-trip inspection step to verify that the spring-activated parking brake can effectively hold the vehicle stationary.
- Performed after building full air pressure.
- Vehicle in low gear, gently attempt to move.
- Should hold vehicle without any movement.
Memory trick: Parking brake's might, holds the truck tight!