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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 tractor is equipped with a Fifth Wheel that pivots as you back up under, or pull out from under, a trailer. A kingpin on the trailer slides up into the Fifth Wheel and the Fifth Wheel 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 Fifth Wheel. Following is the procedure for coupling and uncoupling a single trailer.


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

Position tractor directly in front of trailer. Approach with the trailer on your left and begin turning out just as the tractor’s front bumper approaches the corner of the trailer. Use both mirrors to line up with the trailer. Try to get an even amount of trailer to show in each mirror. On a 102 wide trailer, the trailer should stick out just a little bit farther than the tires of the tractor on both sides. Remember the bobtail tractor will back just like a car.

Back slowly until you are approximately one quarter of the way under the Fifth Wheel 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 tractor backed underneath it and:

* The kingpin went entirely over the Fifth
Wheel or

* The jaws of the Fifth Wheel only caught the bottom part of the kingpin.

With the first type of High Hook, the difficulty will be in getting the tractor away from the trailer. You will probably have to crank the trailer up as far as possible and dump the tractor’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 Fifth Wheel goes under the trailer, and check the height of the trailer. If the trailer does not touch the Fifth Wheel before a quarter to halfway up the Fifth Wheel, you need to crank the trailer down. There should never be air between the Fifth Wheel 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 fifth wheel 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 Fifth Wheel 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 tractor is backed under it.

Check side to side alignment of the kingpin to the Fifth Wheel jaws. If you are more than a couple of inches off, reposition the tractor. You may need to get underneath the trailer, directly behind the kingpin to see if alignment is okay.

Back tractor until (slow, easy) Fifth Wheel engages kingpin and locks. (Roll window down and listen.)

Pull gently forward twice, in first gear, to test connections.

Apply tractor brake. (Pull yellow button out.)

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

Attach gladhands (airlines) and electrical cord.

Raise and secure landing gear. Crank arm in: low gear. Crank arm out: high gear. Clockwise: raise trailer. Counterclockwise: lower trailer. (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. (Pull out red and yellow buttons.)

Lower landing 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 3-4 turns in low gear. With a loaded trailer, when the dollies touch the ground, crank another 6-8 turns in low gear.

Disconnect and store air lines and electrical cable.

Pull Fifth Wheel Release Arm. Some Fifth Wheels are easier to release than others. You can buy a Fifth Wheel 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 fifth wheel 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 tractor partially clear of trailer, leaving the back part of Fifth Wheel 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 tractor than on its nose.

Pull tractor completely clear of trailer.

Flip the dump valve switch back over. (If applicable)

In the winter the Fifth Wheel 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 tractor brakes, putting the transmission in a low gear and pulling forward slightly until you feel resistance. If the jaws are not locked properly, the tractor will pull out from under the trailer.




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