Coupling and Uncoupling - Tractors to Trailers

couplingCoupling and uncoupling tractors and trailers can present serious hazards if precautions are not taken. Failure to follow proper procedures can cause tractor runaway or trailer rollaway situations that result in costly equipment damage or serious, even fatal injuries. 

Understanding how to correctly couple and uncouple a vehicle is a basic skill required of any professional driver. In fact, FMCSR Part 383.111 requires that all commercial motor vehicle operators have knowledge in “procedures for proper coupling and uncoupling a tractor to semi-trailer.” 


 -When trailer brakes are not functioning, the trailer can be pushed into an obstruction and/or into the driver or a bystander. 

- When the ground is not firm for coupling/uncoupling, the trailer can fall and become damaged and/or fall onto the driver or a bystander. 

- When trailer wheels are not chocked, the trailer may roll or be pushed into an obstruction and/or into the driver or a bystander.

- When climbing onto the tractor during coupling, the driver could fall due to slippery surfaces. 

- If the driver works under an unsupported trailer (no jackstand or tractor under the trailer’s nose) he or she could become injured if the landing gear collapses and the trailer drops to the ground.

- The trailer kingpin may be set too shallow or the tractor frame may be too long. Damage to the tractor, trailer or landing gear may result. Occasionally the tractor frame may have enough clearance, but if the tractor is equipped with mud flaps behind the drive axles, there may not be enough clearance when turning, resulting in damaging the mud flap hangers, or the supports for the landing gears.  

Recommended Coupling and Uncoupling Procedures 

Drivers need to be trained in the safe procedures for coupling and uncoupling their vehicles. It is important to know the differences among vehicle manufacturers and to refer to manufacturer instructions for details on procedures for the vehicles you operate. Consider the following ‘general’ coupling and uncoupling procedures and apply and/or adapt these procedures for your vehicles as individual circumstances warrant. 

Prior to coupling: 

- Make sure the parking area is level and firm enough to support trailer and landing gear. 

- Make sure enough room is available to maneuver the vehicle safely, and the area around vehicle is clear and unobstructed. 

- Make sure enough light is available to perform procedure safely.

-Inspect the fifth wheel for damaged or missing parts, and grease the wheel plate as required.

-Check to see if the fifth wheel is in the proper position for coupling (ensure the wheel is tilted down toward the tractor, jaws are open, safety unlocking handle is in the automatic lock position, and trailer kingpin is not bent or broken)

- Make sure trailer wheels are chocked or spring brakes are on, and that cargo is secured against movement.

When Coupling Trailers 

- Reverse tractor slowly in a straight line until the fifth wheel touches the trailer. Don’t hit the trailer. 

- Stop the tractor. Put the parking brake on and place the transmission in neutral. Remove the keys.

- Check trailer height. Raise or lower the trailer until the kingpin and fifth wheel are aligned.

- Attach tractor emergency and service air lines to the trailer. Make sure the air lines are safely supported where they won’t be crushed or caught while the tractor is backing under the trailer.

- From the cab, supply air to the trailer brake system. When you are sure the trailer brakes are working, lock them.

- Back under the trailer using the lowest reverse gear. Avoid hitting the kingpin too hard. Stop when the kingpin is locked into the fifth wheel.

- Raise the trailer landing gear slightly off ground. Pull the tractor gently forward while trailer brakes are still locked to check that the trailer is locked onto the tractor.

- Put the transmission in neutral, put on the parking brakes, shut off the engine and remove the key. Inspect the coupling. Make sure there is no space between the upper and lower fifth wheel; that fifth wheel jaws are around the kingpin; that locking lever is in the “lock” position; and that the safety latch is in position over the locking lever.

- If coupling isn’t right, don’t drive the coupled unit until problems are fixed.

- Plug/connect the electrical line and check electrical and air lines for damage. Be sure lines will not hit any moving parts of the vehicle.

- Raise trailer supports (landing gear). Never drive with landing gear only part-way up. After raising the landing gear, support the crank handle.

- Remove and store wheel chocks in a safe place.

- Complete all necessary visual and functional checks before moving the unit.

When uncoupling, you should normally follow the coupling procedure in reverse. 

For more information on coupling and uncoupling procedures, refer to the Commercial Drivers License (CDL) Manual. The CDL Manual was created to teach truck drivers the FMCSR requirements. Information in the CDL Manual is required knowledge for any person driving a truck with a commercial drivers license. The model CDL Manual is produced by the American Association of Motor Vehicle Administrators (AAMVA). 

Source:  AAMVA model CDL Manual, 2005 (issued August 2006).