Coupling and Uncoupling

Coupling and uncoupling correctly is basic to the safe operation of tractor-trailers. Incorrect coupling and uncoupling can be dangerous and cause unnecessary equipment damage and downtime. The basic steps for coupling a tractor to a trailer are as follows:

Step 1. Inspect fifth wheel

Check for damaged and missing parts.

Ensure the mounting to the tractor is secure and there are no cracks in the frame.

Ensure the fifth wheel plate is greased. Failure to keep the fifth wheel plate lubricated could cause steering problems because of friction between the tractor and the trailer.

Ensure the fifth wheel is in proper position for coupling by completing the following checks:

1. Ensure the wheel is tilted down towards the rear of the tractor.

2. Ensure the locking jaws are open.

3. If equipped with a sliding fifth wheel assembly, ensure it is locked in position.

4. Ensure the trailer kingpin is not bent or broken.

Step 2. Inspect area and chock wheels

Ensure the area around the tractor and trailer are clear of obstacles.

Check the trailer wheels and ensure chocks are in place and the spring brakes are engaged.

Check all cargo (if any) and ensure it is secured from movement due to the tractor being coupled to the trailer.

Step 3. Position tractor

Position the tractor directly in front of the trailer.

(Backing under the trailer at an angle could push the trailer sideways and bend or break the landing gear.)

. Check the position of the tractor by using both

outside mirrors and by looking down both sides of the trailer.

Step 4. Back slowly

l Back slowly until the fifth wheel just touches the trailer.

Step 5. Secure tractor

l Apply the parking brake.

l Place the manual transmission in neutral; if an automatic transmission, place in park.

l Place wheel chocks.

Step 6. Check height of trailer

. The trailer should be low enough to allow it to be raised slightly by the tractor when the tractor is backed under it. Raise or lower the trailer as needed.

CAUTION

If the trailer is too low, the tractor may strike and cause unnecessary damage to both the rear of the tractor and the nose of the trailer. If the trailer is too high, it may not couple correctly.

. Ensure the kingpin and fifth wheel are aligned.

Step 7. Connect air lines to trailer 

Inspect rubber grommets in the glad hands for wear and tear.

Connect the tractor emergency air line to the trailer emergency glad hands.

Connect the tractor service air line to the trailer service glad hands.

Ensure air lines are safely supported so they cannot be crushed or caught while the tractor is backing under the trailer.

Step 8. Supply air to trailer 

l From the cab, push in the "air supply" knob to supply air to the trailer brake system. Military tractors are sometimes equipped with shutoff valves that must be opened to supply air to the trailer brake system.

l Check the air pressure gauge and wait until the air pressure is normal.

l Apply and release trailer brakes, listen for the sound of the trailer brakes being applied and released. You should hear the brakes move when applied and air escape when the brakes are released.

l Check the air pressure gauge for signs of major air loss.

Step 9. Lock trailer brakes

. Pull out the "air supply" knob or apply the trailer hand valve on the steering column to lock the trailer brakes.

Step 10. Back under the trailer

l Use the lowest reverse gear.

l Back the tractor under the trailer until the kingpin is locked into the fifth wheel.

l Pull the tractor gently forward while the trailer brakes are still engaged ensuring the trailer kingpin is locked into the locking jaws of the fifth wheel.

Step 11. Inspect coupling

. Place the transmission in neutral, if manual; in park, if an automatic transmission.

. Engage parking brakes.

. Disengage the trailer hand valve.

NOTE: Depending on your location, you may want to shut off the engine and take the key with you to prevent someone from moving the truck while you are under it.

. Inspect the area around the fifth wheel. Make sure there is no gap between the upper and lower fifth wheel. If there is a gap, something is wrong. The kingpin may be on top of the closed locking jaws; if so, the trailer can come loose easily.

Figure 7-16.-Trailer kingpin.

L Go under the trailer and look into the back of the fifth wheel. Ensure the fifth wheel locking jaws have closed around the shank of the kingpin (fig. 7-16).

. Check that the locking lever pin is in the "lock" position (fig. 7-17).

. Ensure the safety catch is in position over the locking lever pin (if so equipped).

Step 12. Connect the electrical cord and check air lines

. Plug the electrical cord into the trailer (fig. 7-18) and fasten the safety catch.

. Inspect both air lines and electrical lines for signs of damage.

. Ensure air and electrical lines do not contact any moving parts of the vehicle.

Step 13. Raise landing gear

L Use the low gear (if so equipped) to begin raising the landing gear. Once free of weight, switch to the high gear range.

L Raise the landing gear all the way up. Driving with the landing gear part way up is not a good practice because it may catch on railroad tracks or other obstacles.

L Secure the crank handle safely after the landing gear is raised.

Figure 7-17.-Locked fifth wheel.

Figure 7-18.-Electrical connector.

. Check the rear of the tractor frame and the landing gear for enough clearance to make turns.

. Ensure there is enough clearance between the top of the tractor tires and the nose of the trailer.

Step 14. Remove trailer wheel chocks o Remove and store wheel chocks in a safe place.

The basic steps for uncoupling a tractor from a trailer are as follows:

Step 1. Position tractor and trailer

Ensure the parking area surface can support the weight of the trailer.

Ensure the tractor is lined up with the trailer, if at all possible, because pulling out at an angle can bend and damage the landing gear.

Step 2. Ease pressure on locking jaws

l Shut off trailer air supply or engage the trailer hand valve to lock the trailer brakes.

l Ease pressure on the locking jaws by backing up gently. (This procedure helps you release the fifth wheel locking lever.)

l Apply the parking brakes while the tractor is backing; this holds the tractor in place with the pressure of the kingpin off the locking jaws.

Step 3. Lower the landing gear l Chock the trailer wheels.

If the trailer is empty: lower the landing gear until it makes firm contact with the ground.

If the trailer is loaded: after the landing gear makes firm contact with the ground, turn the crank in low gear a few extra turns; this lifts some weight off the tractor suspension.

NOTE: Do not lower the landing gear so low that it lifts the trailer off the fifth wheel because doing this makes it harder to couple and uncouple.

Step 4. Disconnect electrical cable

Disconnect the electrical cable and hang the cable with the plug down to prevent moisture from entering it.

Ensure the electrical cable is supported so it will not be damaged while driving the tractor.

Step 5. Unlock fifth wheel

Raise the safety catch over the locking pin (if so equipped).

Pull the release handle to the "open" position.