Before you can pull a trailer, you must join it to the tractor. You will back the tractor up to the trailer so the tractor fifth wheel and the trailer king pin connect without damaging the tractor or trailer or moving the trailer backward. A proper coupling requires you to centre the king pin in the fifth wheel within a small margin of error. One important consideration is vertical alignment, the level of the fifth wheel compared to the level of the king pin. You will achieve proper vertical alignment by adjusting the height of the trailer using the landing gear.
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Measure the distance between the landing gear and the king pin. Measure the distance from the centre of the fifth wheel to the rear of the tractor's frame and mud flap brackets. Compare the two measurements to make sure the tractor and the trailer are compatible. A short trailer may not have the distance that could handle the rear-end length of some tractors without damaging the mud flap brackets. In some cases sliding the fifth wheel rearward may provide the needed distance.
Find the landing gear crank. It's usually at the left side of the trailer. Unlatch the landing gear crank handle if it is latched in the crank holder. On most trailers, you turn the landing gear crank clockwise to extend the landing gear legs and raise the trailer. You turn the landing gear crank counterclockwise to retract the legs and lower the trailer. Raise or lower the trailer with the landing gear so the coupling surface of the trailer is aligned to just about the middle of the fifth wheel skid ramps. Crank the landing gear up or down until the trailer is low enough so the tractor will lift the trailer up slightly when you back the tractor under it.
Drive the tractor slowly in reverse to back the tractor under the trailer. You will feel the weight of the trailer being transferred to the tractor as the apron of the trailer upper coupler slides up the skid ramps of the tractor fifth wheel. Continue backing slowly until progress is stopped by the king pin locking into the jaws of the fifth wheel. If the trailer is fairly light, you'll be able to get the tractor under it without much effort. If the trailer is heavily loaded, you will feel some resistance.
Stop backing up if the tractor won't go under the trailer. Don't force it. If the trailer is a little too low and you can't get the tractor under it without a lot of effort, stop and get out of the tractor. At the trailer, crank the landing gear clockwise to raise the trailer up a little more. This is not all that easy with a loaded trailer, but it's still the best solution.
Tips and warnings
- Most trailer gear boxes have two speeds. Use low gear while the landing legs are supporting most of the trailer's weight. Use high gear when the trailer is empty or its loaded weight rests on the fifth wheel.
- Always secure the crank handle when you're done using it.
- If the trailer is too far below the fifth wheel level, the king pin will hit the tractor frame. If the trailer is too high, the king pin could slide right over the top of the fifth wheel when you try to back under it. You could damage the rear of the tractor that way.
- Although they are built of hardened steel the gears can become damaged if you are not careful.
- A crank handle that is unsecured can swing freely while the trailer is moving and it could hit a nearby vehicle or passing pedestrian.
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