CDL General Knowledge TestCombination Vehicles (if applicable)Medium
A driver is preparing to uncouple a combination vehicle. After lowering the landing gear until it makes firm contact with the ground, what is the next crucial step before completely separating the tractor from the trailer?
- ADisconnect the electrical cord and air lines.
- BRelease the fifth wheel locking jaws.
- CMove the tractor forward until the kingpin clears the fifth wheel.
- DRaise the landing gear slightly to take weight off the tractor.
Show answer & explanationAnswer & explanation
Correct answer: D. Raise the landing gear slightly to take weight off the tractor.
After the landing gear makes firm contact, it's essential to raise it slightly. This lifts the trailer a small amount, taking the weight off the tractor's fifth wheel. This slight elevation ensures that the kingpin will clear the fifth wheel skid plate when the tractor pulls away, preventing damage to both components and making separation smoother.
Why the other options are wrong
- A. These should be disconnected, but after the weight is off the fifth wheel.
- B. The fifth wheel release is typically done after lifting the trailer slightly.
- C. Moving the tractor is the final step, after all connections are released and weight is off.
Uncoupling: Weight Transfer
During uncoupling, after the landing gear contacts the ground, the trailer must be slightly raised to transfer its weight off the tractor's fifth wheel, facilitating a clean separation.
- Prevents damage to fifth wheel and kingpin.
- Ensures smooth uncoupling.
- A crucial step before releasing the fifth wheel jaws.
Memory trick: Lower, Lift, Disconnect, Release, Drive.