How to Hook Up a 5th Wheel


Commercial tractor trailers use a locking mechanism to connect the trailer to the truck cab. This connection is called a fifth wheel hitch that incorporates a "king pin" into a locking collar for a secure connection during operation. Made for recreational vehicles as well, the fifth wheel trailer hitch is the most common type of connector for vehicles that tow heavy loads over the streets of America and around the world. Connecting a trailer to a truck using a fifth wheel hitch is easy. Simply get in the truck and go in reverse to get the job done quickly.

Things You'll Need

  • Truck cab Trailer Fifth wheel hitch Adjustable trailer legs
  • Grease the locking plate so that the trailer slides into locking position without rubbing two metals together that are not lubricated. The king pin that is on the trailer will slide into the locking mechanism and the king pin plate will ride on top of the locking mechanisms raised support plate. when the vehicle turns the king pin and the lock will be able to rotate with the turns and the trailer can slide over the locking plate easily with the grease added before a fifth wheel hook up.

  • Center the truck cab in front of the trailer. Park the truck and check that the height of the trailer is high enough for the truck cab to slide underneath and catch the king pin under the trailer. The king pin under the trailer will need to slide inside the cut-out slot of the locking mechanism and be captured by the locking bar. Pull the armature that opens the locking mechanism located on the side of the truck cabs locking plate. Pull it completely out and the lock will be opened. Once the king pin has entered the locking mechanism, this arm will close, securing the trailer to the truck cab during travel.

  • Raise or lower the trailer to the correct height to enter the locking mechanism and then get in the truck and start the vehicle. Place the truck in reverse and accelerate the vehicle under the raised trailer and inline with the king pin to seat the king pin into the fifth wheel locking arm securing the trailer to the truck. When the king pin is correctly inserted into the locking mechanism, the armature that released the lock will engage and a loud click will be heard from inside the passenger cabin. Put the truck in gear and move forward slightly to insure that the king pin is locked into the mechanism. if the truck pulls away without the trailer, repeat the process of backing up into the king pin until it seats correctly and the locking mechanism engages the trailer firmly to the truck.

  • Place the truck in park while it's running. The air compressors need to be working so that when the trailer is connected to the compressed air system of the vehicle, the brakes will activate and be able to be used in unison with the truck brakes. Step around the back of the truck cabin and connect the air lines that come from the trailer. Connect the airlines and let enough pressure build up to release the trailer brakes. A signal within the truck cab will alert the driver to the compressed air inside the brakes and when they are ready for use.

  • Use the hand crank to lift the trailer legs from supporting the trailer above the ground. When the trailer legs are raised, the weight of the trailer is transferred to the tow vehicle and the fifth wheel connection is activated. Test the fifth wheel connection by making sure the locking mechanism armature is completely locked in place, and the trailer does not become dislodged from the truck cabin. Reverse the process to remove a trailer from a fifth wheel hitch when leaving a recreational vehicle or tractor trailer behind.

Tips & Warnings

  • Jerk the locking mechanism armature hard to dislodge a locking arm from the fifth wheel receiver plate. The spring that activates this armature is very firm and takes a hard pull or push sometimes to seat it or unlock it correctly.
  • TRAILER LEGS! Always check to be sure the fifth wheel hitch is secured around the king pin before driving away. The locking mechanism may not seat properly and the trailer will remain behind if this is allowed to happen. Check and recheck the fifth wheel connection prior to driving away with a fully loaded trailer or recreational vehicle that has its supporting legs raised for travel.

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  • Photo Credit The Bernardos
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