Safety First 07: Coupling and Uncoupling

Safety First · Lesson 07 of 30 · Basic Operation
Free safety education based on the federal Entry-Level Driver Training (ELDT) theory curriculum. This is not certified ELDT training and does not count toward a CDL.

The seventh unit of the federal Class A theory curriculum is Coupling and Uncoupling. It covers how to connect a tractor to a semitrailer, and how to disconnect them, safely.

If a trailer is not coupled correctly, it can come loose. The steps below follow the sequence in state CDL manuals based on the national model. Learn the full procedure in your own state manual.

What this unit covers

Under 49 CFR Part 380, Appendix A, this unit provides instruction for driver-trainees to develop the skills necessary to conduct the procedures for safe coupling and uncoupling of combination vehicle units, as applicable.

1. The parts you are connecting

  • Fifth wheel. The coupling device on the tractor. Its locking jaws close around the shank of the trailer's kingpin.
  • Kingpin. The pin under the front of the trailer that locks into the fifth wheel.
  • Air lines and glad hands. The service line (also called the control line or signal line) carries air, which is controlled by the foot brake or the trailer hand brake. The emergency line (also called the supply line) supplies air to the trailer air tanks and controls the trailer emergency brakes. Glad hands are the coupling devices that connect these lines. Emergency lines are often coded red, to keep them from being mixed up with the blue service line.
  • Electrical cord. Connects the trailer's lights and electrical system to the tractor.
  • Landing gear. The front trailer supports that hold up the trailer when it is not coupled.

2. Coupling, step by step

  1. Inspect the fifth wheel. Check for damaged or missing parts and a secure mounting with no cracks in the frame. Make sure the fifth wheel plate is greased as required, and that the fifth wheel is in the proper position for coupling: tilted down toward the rear of the tractor, jaws open, and the safety unlocking handle in the automatic lock position. If it is a sliding fifth wheel, make sure it is locked. Make sure the trailer kingpin is not bent or broken.
  2. Inspect the area and chock the wheels. Make sure the area around the vehicle is clear. Be sure the trailer wheels are chocked or the trailer spring brakes are on. Check that any cargo is secured.
  3. Position the tractor. Put the tractor directly in front of the trailer. Never back under the trailer at an angle. Check the position using the outside mirrors.
  4. Back slowly. Back until the fifth wheel just touches the trailer. Do not hit the trailer.
  5. Secure the tractor. Put on the parking brake and put the transmission in neutral.
  6. Check the trailer height. The trailer should be low enough that it is raised slightly by the tractor when the tractor is backed under it. Raise or lower the trailer as needed, and check that the kingpin and fifth wheel are aligned.
  7. Connect the air lines. Check the glad hand seals. Connect the tractor emergency line to the trailer emergency glad hand, and the tractor service line to the trailer service glad hand. Support the lines so they will not be crushed or caught while you back under the trailer.
  8. Supply air to the trailer. Push in the air supply knob, or move the tractor protection valve control to the "normal" position. Wait until the air pressure is normal. Check for crossed air lines: shut off the engine so you can hear the brakes, apply and release the trailer brakes, and listen for the sound of the trailer brakes being applied and released. Check the air pressure gauge for signs of major air loss. When you are sure the trailer brakes are working, start the engine and make sure the air pressure is normal.
  9. Lock the trailer brakes. Pull out the air supply knob, or move the tractor protection valve control to the "emergency" position.
  10. Back under the trailer. Use the lowest reverse gear. Back slowly to avoid hitting the kingpin too hard, and stop when the kingpin is locked into the fifth wheel.
  11. Check the connection. Raise the trailer landing gear slightly off the ground. With the trailer brakes still locked, pull the tractor gently forward to make sure the trailer is locked onto the tractor.
  12. Secure the vehicle. Put the transmission in neutral, put on the parking brake, shut off the engine, and take the key with you so no one moves the truck while you are under it.
  13. Inspect the coupling. Use a flashlight if needed. There should be no space between the upper and lower fifth wheel. Look into the back of the fifth wheel and make sure the locking jaws are closed around the shank of the kingpin, not the head. Check that the locking lever is in the lock position and the safety latch is in position over the locking lever. If the coupling is not right, do not drive the coupled unit. Get it fixed.
  14. Connect the electrical cord and check the lines. Plug the electrical cord into the trailer and fasten the safety catch. Check the air and electrical lines for damage, and make sure they will not hit any moving parts of the vehicle.
  15. Raise the landing gear. Use the low gear range to begin raising the landing gear, then switch to the high gear range once the trailer's weight is off. Raise the landing gear all the way up. Never drive with the landing gear only part way up. Secure the crank handle. After raising the landing gear, check for enough clearance between the rear of the tractor frame and the landing gear, and between the top of the tractor tires and the nose of the trailer.
  16. Remove the trailer wheel chocks and store them in a safe place.

3. Uncoupling, step by step

  1. Position the rig. Make sure the surface of the parking area can support the weight of the trailer. Have the tractor lined up with the trailer. Pulling out at an angle can damage the landing gear.
  2. Ease pressure on the locking jaws. Shut off the trailer air supply to lock the trailer brakes. Back up gently to ease pressure on the fifth wheel locking jaws, then put on the parking brakes while the tractor is pushing against the kingpin.
  3. Chock the trailer wheels if the trailer does not have spring brakes, or if you are not sure.
  4. Lower the landing gear. 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 to take some weight off the tractor. Do not lift the trailer off the fifth wheel.
  5. Disconnect the air lines and electrical cable. Disconnect the air lines from the trailer and connect the glad hands to the dummy couplers at the back of the cab, or couple them together. Hang the electrical cable with the plug down to prevent moisture from entering it. Make sure the lines are supported so they will not be damaged while driving the tractor.
  6. Unlock the fifth wheel. Raise the release handle lock and pull the release handle to the "open" position. Keep your legs and feet clear of the rear tractor wheels.
  7. Pull the tractor partially clear. Pull the tractor forward until the fifth wheel comes out from under the trailer. Stop with the tractor frame still under the trailer. This prevents the trailer from falling to the ground if the landing gear collapses or sinks.
  8. Secure the tractor. Put on the parking brake and put the transmission in neutral.
  9. Inspect the trailer supports. Make sure the ground is supporting the trailer and the landing gear is not damaged.
  10. Pull the tractor clear. Release the parking brakes, check the area, and drive the tractor forward until it clears the trailer.

4. Container chassis

In drayage, the trailer is often an intermodal chassis carrying a container. Before taking intermodal equipment over the road, federal rules (49 CFR 392.7(b)) require the driver to inspect specific components, including air line connections, hoses, and couplers, and the king pin upper coupling device. Lesson 03 covers the full list.

Quick check

  1. After backing under the trailer, how does a driver check the connection? (Answer: raise the landing gear slightly off the ground, then, with the trailer brakes still locked, pull the tractor gently forward.)
  2. Before going under the trailer to inspect the coupling, what should the driver do with the engine and key? (Answer: shut off the engine and take the key.)
  3. When uncoupling, why should the tractor stop with its frame still under the trailer? (Answer: to keep the trailer from falling if the landing gear collapses or sinks.)

Find every Safety First lesson under DRIVE.

This lesson is general education, not legal advice. Follow the coupling and uncoupling procedures in your state CDL manual, your training provider, and your carrier, and confirm current rules with FMCSA. Drivers getting their first Class A or Class B CDL, upgrading from Class B to Class A, or getting a hazardous materials, passenger, or school bus endorsement for the first time must, with limited exceptions, complete entry-level driver training from a provider listed on FMCSA's Training Provider Registry.

Sources

FLY YOUR WHEELS!

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