CDL · Combination vehicles
During coupling, your tractor is in front of the semitrailer but not yet under it. What do you connect before backing under?
Correct answer: The service and emergency air lines.
Answer options
- AThe service and emergency air lines Correct
- BNothing until the fifth wheel has locked
- CThe electrical cord for the trailer
Why
Hooking up the air lines first lets you send air to the trailer and check its brakes before the tractor goes under. The electrical cord is plugged in later, after the coupling has been locked and inspected.
About this question
Topic: Combination vehicles License: CDL
Part of these practice sets:
Where it applies: Asked in every state.
Practice the whole set
This question is part of Trailer Air Lines and Coupling (28 questions). Take the full set and check your score.
Practice Trailer Air Lines and CouplingMore questions from Trailer Air Lines and Coupling
- What must you confirm right before backing the tractor under a trailer?
- When you drive a tractor with no trailer attached, why should its glad hands be locked together or onto dummy couplers?
- Which sequence is correct for testing the trailer service brakes?
- Before coupling, how high should the trailer sit compared with the converter dolly's fifth wheel?
- As air pressure drops, a tractor protection valve shuts by itself at a level set by its manufacturer. That level usually falls within which range?
- Before the tractor backs under a semitrailer during coupling, how high should the front of the trailer be?
- In which situation may a parked combination vehicle be held by the trailer hand valve alone?
- On a tractor-trailer, what are glad hands used for?
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