LGV Coupling and Uncoupling 2

Question 1

What is the correct first step when uncoupling a semi-trailer?

Accepted Answer

Apply the trailer parking brake and lower the landing gear until they are firmly supporting the trailer weight

Answer

The first step is to apply the trailer parking brake and lower the landing gear until they take the weight of the trailer. This ensures the trailer is stable and supported before the tractor is removed. Never release the coupling before the trailer is independently supported.

Question 2

What could happen if a driver fails to perform a proper tug test after coupling?

Accepted Answer

The coupling may not be fully locked, and the trailer could separate from the tractor while driving

Answer

Without a tug test, the 5th wheel jaws may appear closed but not be fully locked around the kingpin. A partial engagement could release under load, causing the trailer to separate from the tractor at speed — an extremely dangerous situation that has caused fatal incidents.

Question 3

What should a driver check about the trailer kingpin before coupling?

Accepted Answer

That it is not worn, bent, or cracked, and that the trailer plate is not damaged

Answer

The kingpin should be inspected for wear, bending, cracking, or damage. The trailer coupling plate should also be checked for cracks or distortion. A worn or damaged kingpin may not lock securely in the 5th wheel jaws.

Question 4

Why is it important to ensure the trailer is at the correct height before coupling?

Accepted Answer

If too high, the kingpin may ride over the jaws; if too low, it may not engage properly or could damage the trailer plate

Answer

The trailer must be at the correct height for the 5th wheel to slide smoothly under the trailer plate and for the kingpin to drop into the jaws. Too high and the kingpin may not engage; too low and the 5th wheel could strike and damage the trailer underside.

Question 5

When should the electrical connections (suzi coils) be connected during coupling?

Accepted Answer

After the mechanical coupling is confirmed secure and air lines are connected

Answer

Electrical connections (for lights, ABS, EBS) should be connected after the mechanical coupling and air lines are confirmed secure. This ensures the trailer lights and electronic brake systems are functional before driving.

DVSA UK Driving Theory Practice Test

DVSA UK Driving Theory Practice Test

LGV Coupling and Uncoupling 2