CDL Combination Vehicles TestCombination Vehicle Air BrakesMedium
When inspecting the air lines on a combination vehicle, a driver finds that the service (blue) air line on the trailer has a significant leak. What is the most immediate and critical consequence of this specific leak?
- AThe trailer's emergency (spring) brakes will automatically apply.
- BThe tractor's parking brakes will automatically apply.
- CThe trailer's service brakes will not apply properly.
- DThe air compressor will continuously run, leading to overheating.
Show answer & explanationAnswer & explanation
Correct answer: C. The trailer's service brakes will not apply properly.
The service (blue) air line supplies air to the trailer's service brake chambers. A significant leak in this line would prevent air pressure from reaching the service brakes, making them unable to apply properly.
Why the other options are wrong
- A. The emergency (red) line supplies air to release the spring brakes. A leak in the service line does not cause the emergency brakes to apply, unless the system pressure drops below a critical point, but the primary and most immediate effect is on service brake application.
- B. A leak in the service line affects trailer service brakes, not the tractor's parking brakes directly.
- D. While the compressor might run more, the immediate and critical consequence is brake failure, not compressor overheating.
Service Air Line (Blue)
The air line, typically blue, that carries air from the tractor's foot valve or hand valve to the trailer's service brake chambers for normal braking.
- Connects to trailer service brakes.
- Controls normal braking on the trailer.
- A leak prevents service brake application.
Memory trick: Blue for service, red for emergency, keep them tight to stay free.