HC (Semi trailer)

Uncouple/ Recouple

Coupling & Uncoupling

It is not hard to do… but… there is no margin for error!

Coupling and uncoupling (or hooking and unhooking) is a simple and fast process once you get the hang of it, but do it wrong and the results can be catastrophic. Just about the best insurance against dropping a trailer in its landing gear or high hooking (explained below), is to complete the procedure exactly the same every single time.
The Truck /Prime Mover is equipped with a turntable (that might pivot as you back up under, or pull out from under, a trailer). A kingpin on the trailer slides up into the turntable and the turntable jaws latch closed, around the shank of the kingpin. In order to open the jaws, you must pull a Release Arm on the side of the turntable . Following is the procedure for coupling and uncoupling a single trailer.


Inspect turntable for damage and proper lubrication. If a turntable does not have enough grease, it can make turning more difficult. Ensure that the jaws are open and the turntable is tilted down towards the rear of the Truck /Prime Mover. (Note that the graphic on this page shows a turntable without any tilt. This should not be so when the Truck /Prime Mover is without a trailer – it should tilt down, towards the back of the Truck /Prime Mover.)

Position Truck directly in front of trailer. Approach with the trailer visible equally in both mirrors . Use both mirrors to line up with the trailer. Try to get an even amount of trailer to show in each mirror. On our trailer, the trailer should line up with the tray of the Truck /Prime Mover on both sides. Remember the bobtail Prime Mover will back just like a car.

Back slowly until you are approximately one quarter of the way under the turntable and no more than halfway under. Being able to tell where this point is may take some practice. It is better to stop too soon than too late, though! Backing under a trailer when the trailer is too high can lead to a “High Hook.”

A High Hook occurs when the trailer was too high when a Truck /Prime Mover backed underneath it and:
* The kingpin went entirely over the turntable l or

* The jaws of the turntable only caught the bottom part of the kingpin.

With the first type of High Hook, the difficulty will be in getting the Truck /Prime Mover away from the trailer. You will probably have to crank the trailer up as far as possible and dump the Truck /Prime Mover’s suspension. With the second type of High Hook, it may be difficult to get unhooked, but what is worse is that it is not always easy to even be aware this type of High Hook has occurred. A trailer can be pulled with this sort of High Hook situation for quite some time but the ending result is that it is most likely going to fall off. To avoid having this happen to you, make it a habit to get out of the truck every single time you hook up, before the turntable goes under the trailer, and check the height of the trailer. If the trailer does not touch the turntable before a quarter to halfway up the 5th wheel/turntable , you need to crank the trailer down. There should never be air between the turntable and the apron of the trailer.

The first photo shows a trailer that is too high. The second photo shows a trailer at perfect height - not too low, not too high. In truth, the first photo probably would not result in a high hook, but it is always better to be safe than to be sorry... And boy would you be sorry if you made a turn and your trailer fell off. The last photo, which is somewhat difficult to see, I admit, is of the alignment of the kingpin in relation to the 5th wheel/turntable jaws. (Click any photo to see enlarged) This kingpin is directly lined up. This photo was taken from under the trailer while the trailer was in the position shown in the second photo.

Get out of cab, check turntable height and adjust if necessary by cranking the trailer down with the landing gear. The trailer should be low enough to allow it to be lifted up slightly as the Truck /Prime Mover is backed under it.

Check side to side alignment of the kingpin to the turntable jaws. If you are more than a couple of cm’s off, reposition the Truck /Prime Mover. You may need to get underneath the trailer, directly behind the kingpin to see if alignment is okay.

Back Truck /Prime Mover until (slow, easy) turntable jaws engages kingpin and locks. (Roll window down and listen.)

Pull gently forward twice, in 1st or 2nd gear, to test connections (tug test)

Apply Truck /Prime Mover brake. (Pull UD black lever up) (Volvo p’brake lever down)

Get out and inspect 5th wheel/turntable jaws to ensure that they have locked around the kingpin. Check that the release arm has gone from the out (unlocked) position to the (IN) locked position.

Attach (airlines) and electrical cord. …….

Raise and secure landing gear. Crank arm in: high gear. Crank arm out: low gear.. (Some trailers will defy these rules so if one way doesn’t work, try the other.)


Park the vehicle. Try to park on a level surface. -- Apply the brakes. Leave motor running or use turbo timer in Volvo Climb out backwards , shut door and go around to LHS and put chocks down under LHS front trailer tyre) Walk around to RHS
Lower landing gear. Land firmly than 8-9 turns in low gear.. When dropping a loaded trailer, you should crank the gear down farther than if you were dropping an empty. With an empty, when the dollies, or landing gear legs, touch the ground, crank another 8-9 turns in low gear. With a loaded trailer, when the legs touch the ground, crank another 12-14 turns in low gear.

Disconnect and store air lines and electrical cable.

Pull turntable jaws Release Arm. (Joss on Volvo _ lift up release tab slide handle forward then pull out) Some turntable s are easier to release than others. You can buy a turntable lever puller for approximately $12-$15 at most truckstops. It is a long metal bar with a hooked end that gives you leverage to make it easier to pull the Release Arm. They also help to keep you cleaner. Some drivers use meat hooks as 5th wheel/turntable pullers but the ones sold at truck stops are usually easier to use because they are longer.

Lower the suspension by flipping the dump valve switch. (If equipped)

Pull Truck /Prime Mover partially clear of trailer, leaving the back part of turntable under trailer.

Wait a moment to be sure trailer is going to stand. If a trailer has to fall, it is better for it to do so on the frame of the Truck /Prime Mover than on its nose.

Pull Truck /Prime Mover completely clear of trailer.
Flip the dump valve switch back over/up . (If applicable)

In the winter the turntable jaws can be rather tricky - it may appear to lock but may not fully do so. Make absolutely sure the jaws have locked by performing a “tug” test and by physically getting underneath the trailer to look at the jaws. Also check that the Release Arm itself goes in upon “hooking” the trailer. A tug test consists of setting the trailer brakes (on), releasing the Truck /Prime Mover brakes, putting the transmission in a low gear and pulling forward slightly until you feel resistance. If the jaws are not locked properly, the Truck /Prime Mover will pull out from under the trailer.