CDL · Combination vehicles
What must you confirm right before backing the tractor under a trailer?
Correct answer: That the brakes on the trailer are locked.
Answer options
- AThat the tractor protection valve control is in the normal position
- BThat the brakes on the trailer are locked Correct
- CThat the air brakes are switched off
Why
Locked trailer brakes keep the trailer from rolling away while the tractor slides under it, so the fifth wheel can catch the kingpin. You set them by pulling out the air supply knob or moving the tractor protection valve control from normal to emergency.
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
- Which sequence is correct for testing the trailer service brakes?
- During coupling, your tractor is in front of the semitrailer but not yet under it. What do you connect before backing under?
- 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?
- When you drive a tractor with no trailer attached, why should its glad hands be locked together or onto dummy couplers?
- In which situation may a parked combination vehicle be held by the trailer hand valve alone?
- Before coupling, how high should the trailer sit compared with the converter dolly's fifth wheel?
- After coupling to a semitrailer, how should you leave the landing gear (front trailer supports) before pulling away?
- Before the tractor backs under a semitrailer during coupling, how high should the front of the trailer be?
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