On a tractor-trailer, if the supply and service lines to the trailer are cross-connected, what may happen?
- The tractor may lose compressed air.
- The trailer parking brakes may not release.
- The service brakes will not work.
- All of the above may happen. ✓
Answer: D. All of the above may happen.
All of the above may happen: cross-connected lines can make the tractor lose air, keep the trailer spring brakes from releasing, and stop the service brakes working properly.
Why this is the answer
The handbook says that when trailer lines are cross-connected, the trailer brakes will not work correctly. It lists three results: the spring brakes may not release, the towing vehicle may lose air, and the service brakes will not function properly. Those three results match the tractor air loss, trailer parking brake release problem and service brake problem given in the choices. Because the handbook gives all three together, the choice covering all of them is correct.
Why the other answers are wrong
- A. The tractor may lose compressed air. — This names only the tractor air loss, while the handbook also lists spring brake release and service brake problems from the same cross-connection.
- B. The trailer parking brakes may not release. — This names only the trailer spring brakes possibly not releasing, missing the tractor air loss and service brake problems the handbook also gives.
- C. The service brakes will not work. — This names only the service brake problem, but the handbook also says the spring brakes may not release and the towing vehicle may lose air.
Remember it
Match red supply to red and blue service to blue; crossed gladhands can upset air supply, spring brake release and service braking together.