DTT HGV Coupling and Uncoupling Trailers 1 — Questions and Answers
Question 1: Before reversing a tractor unit under a semi-trailer for coupling, the fifth wheel should be:
- Locked in the fully closed position
- Clean, greased and in the unlocked (open) position (Correct answer)
- Raised above the trailer height
- Secured with a safety chain
Correct answer: Clean, greased and in the unlocked (open) position
The fifth wheel must be greased and in the open/unlocked position so the kingpin can enter and the jaws can close around it during coupling.
Question 2: The kingpin on a semi-trailer connects with which part of the tractor unit?
- The drawbar hitch
- The fifth wheel coupling plate (Correct answer)
- The rear chassis bumper
- The air brake connector
Correct answer: The fifth wheel coupling plate
The kingpin is the steel pin on the underside of the trailer that locks into the jaws of the fifth wheel coupling plate on the tractor unit.
Question 3: After coupling a trailer, how should you test that the coupling is secure?
- Drive forward 50 metres and check for movement
- Attempt to move forward with the trailer parking brake applied (Correct answer)
- Visually inspect the coupling from outside the cab
- Check the tachograph for any irregularities
Correct answer: Attempt to move forward with the trailer parking brake applied
Moving forward against the applied trailer parking brake confirms the fifth wheel jaws are properly locked around the kingpin without risking movement.
Question 4: When uncoupling a semi-trailer, which sequence of steps is correct?
- Disconnect airlines, lower landing gear, release fifth wheel, drive away
- Apply trailer brake, lower landing gear, disconnect airlines, release fifth wheel, drive away (Correct answer)
- Release fifth wheel, lower landing gear, disconnect airlines, drive away
- Lower landing gear, apply trailer brake, release fifth wheel, drive away
Correct answer: Apply trailer brake, lower landing gear, disconnect airlines, release fifth wheel, drive away
The trailer brakes must be applied and landing gear lowered to support the trailer's weight before the airlines are disconnected and the fifth wheel is released.
Question 5: After connecting the airlines to a trailer, what should you do before departure?
- Immediately proceed on your journey
- Allow air pressure to build and check for air leaks (Correct answer)
- Connect the electrical cable before anything else
- Release all brakes and check for free movement
Correct answer: Allow air pressure to build and check for air leaks
Air pressure must reach the correct level and the system must be checked for leaks to ensure the trailer's braking system will function safely.
Question 6: The red (emergency) airline on a truck-trailer combination controls:
- The service (foot) brakes on the trailer
- The spring (parking/emergency) brakes on the trailer (Correct answer)
- The trailer's air suspension system
- The landing gear electric motor
Correct answer: The spring (parking/emergency) brakes on the trailer
The red airline supplies air to hold the trailer's spring brakes off; if this line breaks or is disconnected, the spring brakes automatically apply.
Question 7: The landing legs of a semi-trailer must be fully raised:
- After the airlines have been connected
- Before the vehicle combination moves off (Correct answer)
- Only when travelling on motorways
- After the destination has been reached
Correct answer: Before the vehicle combination moves off
The landing legs must be fully raised and secured before any movement, as they could otherwise contact the road surface and cause a serious accident.
DTT HGV Coupling and Uncoupling Trailers 1
Before reversing a tractor unit under a semi-trailer for coupling, the fifth wheel should be: