How to Hook Up a Tractor to Its Trailer

Written by kurt schanaman
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How to Hook Up a Tractor to Its Trailer
Connection of a trailer to the tractor of a rig requires mating of the fifth-wheel to the king pin and upper fifth-wheel plate of the trailer, and connection of lines and hoses. (camion australien image by Gilles Paire from

As a Class A truck driver, your responsibilities include following all of the rules set by the Department of Transportation, maintaining logs of operations on a daily basis, and the hooking and unhooking of trailers to the tractor at switch-off points. Connecting a trailer requires proper mating of the fifth-wheel on the back of the tractor to the upper fifth-wheel plate on the underside at the front of the trailer, as well as connecting the power cord and the air supply lines from the tractor to the trailer.

Skill level:

Things you need

  • Tube of grease

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  1. 1

    Back up the tractor until the rear of the tractor frame is within two or three feet of the front lip of the trailer. Exit the tractor, and walk to the rear of the tractor frame. Inspect the height of the trailer to ensure the frame won't hit the front edge of the trailer. If the trailer is too low, get into the tractor and find the air ride switch. Flip the switch to drain the air out of the air ride bags on the rear axles of the tractor so the tractor fifth-wheel is lower than the fifth-wheel plate on the underside of the trailer.

  2. 2

    Back the tractor under the upper plate of the trailer so that the king pin lines up with the king pin slot (groove) in the tractor's fifth-wheel. Back the tractor only until the back part of the fifth-wheel is directly under the front half of the upper plate of the trailer. Exit the cab once again and visually inspect to make sure the king pin is still in line with the slot of the tractor fifth-wheel. If the rear of the tractor frame is lower than the upper plate of the trailer, flip the air ride switch to fill the air bags with air. Allow them to fill until the fifth-wheel of the tractor and the upper plate of the trailer are touching. There can be no space between the two when completing the hookup process. If necessary, lower the trailer jack also, until the fifth-wheel surface on the tractor and the upper plate of the trailer are touching together.

  3. 3

    Open a fresh tube of grease and dump the entire contents onto the fifth-wheel of the tractor. Smear the grease until you cover 3/4 of the entire surface of the fifth-wheel with a generous amount of the grease, and discard the empty tube.

  4. 4

    Back the tractor under the trailer until the tractor won't move backward any further. Get out of the cab and inspect the connection to ensure there are no gaps between the fifth-wheel and the upper plate of the trailer, then get back into the cab. Release the tractor brake valve on the dash (generally the yellow one) by pushing it in, but leave the trailer brake (red knob) set (pulled out). Pull forward with the tractor to make sure the locking jaws of the fifth-wheel have fastened securely to the king pin of the trailer. The tractor shouldn't pull away from the trailer if the connection is successful and no gap is visible between the plates.

  5. 5

    Set the tractor brake (pull it out), and turn off the tractor. Exit the cab, and climb onto the deck plate on the frame just behind the cab of the tractor.

  6. 6

    Connect the power cord to the power socket on the back of the cab of the truck by pushing it into the socket until it snaps into place.

  7. 7

    Connect the air hose connectors (glad hands) to the air nozzles on the back of the tractor cab. The connectors on the hoses are colour coded to match the connectors on the tractor: one pair should be red and one pair should be blue. Beginning with the blue connector on the hose, hold it so it is vertical in relation to the blue connector on the cab of the tractor, and so the two rubber gaskets are facing each other. Press the rubber gaskets together and rotate the hose connector counter-clockwise so the locking arm slides into the locking groove of the connector on the tractor. Rotate until you cannot turn it any further, and repeat this step for the red hose connection.

    How to Hook Up a Tractor to Its Trailer
    Connect the air hose connectors. (Vacuum line image by waynocook from
  8. 8

    Crank up the trailer jack legs, or "landing gear," until fully raised.

  9. 9

    Start the tractor, and allow air pressure to build to between 40.8 and 54.4 Kilogram on the tractor, then release (push in) the tractor air valve and the trailer air valve on the control panel. Allow both the trailer and the tractor air pressure gauges to return once again to between 40.8 and 54.4 Kilogram. Pull forward with the trailer fully connected to ensure the wheels turn freely.

  10. 10

    Set the brakes on both the tractor and the trailer (pull both valve knobs out) and turn on the light switches for the tractor and the trailer. Exit the cab and perform a walk-around inspection of all lights, checking the air pressure in all tires of the rig while walking around the vehicle. Fill any low tires and replace any inoperative lights on the vehicle before leaving the premises.

Tips and warnings

  • Never leave the cab of the tractor unless both tractor and trailer brakes are set. Should the vehicle roll, fatality may occur.
  • Always apply fresh grease to the surface of the tractor's fifth-wheel plate before backing fully under the trailer during connection. Failure to apply grease will permit metal-against-metal wear, causing premature damage to the fifth-wheel and upper plate surfaces.

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