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6.3 Coupling and Uncoupling

Knowing how to couple and uncouple correctly is basic to the safe operation of combination vehicles. Wrong coupling and uncoupling can be very dangerous. General coupling and uncoupling steps are listed below. There are differences between different rigs, so learn the details of coupling and uncoupling the truck(s) you will operate.

Coupling Tractor Semi-Trailers

STEP 1: Inspect Fifth Wheel

  • Check for damaged/missing parts.
  • Check to see that mounting to tractor is secure, no cracks in frame, etc.
  • Be sure that the fifth wheel plate is greased as required. Failure to keep the fifth wheel plate lubricated could cause steering problems because of friction between the tractor and trailer.
  • Check if fifth wheel is in proper position for coupling:
    • Wheel tilted down towards rear of tractor.
    • Jaws open.
    • Safety unlocking handle in the automatic lock position.
  • If you have a sliding fifth wheel, make sure it is locked.
  • Make sure the trailer kingpin is not bent or broken.

STEP 2: Inspect Area and Chock Wheels

  • Make sure area around the vehicle is clear.
  • Be sure trailer wheels are chocked or spring brakes are on.
  • Check that cargo (if any) is secured against movement due to tractor being coupled to the trailer.

STEP 3: Position Tractor

  • Put the tractor directly in front of the trailer (never back under the trailer at an angle because you might push the trailer sideways and break the landing gear).
  • Check position, using outside mirrors, by looking down both sides of the trailer.

STEP 4: Back Slowly

  • Back until fifth wheel just touches the trailer.
  • Do not hit the trailer.

STEP 5: Secure Tractor

  • Put on the parking brake.
  • Put transmission in neutral.

STEP 6: Check 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. (If the trailer is too low, the tractor may strike and damage the nose of the trailer; if the trailer is too high, it may not couple correctly.)
  • Check that the kingpin and fifth wheel are aligned.

STEP 7: Connect Air Lines to Trailer

  • Check glad hand seals and connect tractor emergency air line to trailer emergency glad hand.
  • Check glad hand seals and connect tractor service air line to trailer service glad hand.
  • Make sure air lines are safely supported where they will not be crushed or caught while tractor is backing under the trailer.

STEP 8: Supply Air to Trailer

  • From the cab, push in “air supply” knob or move tractor protection valve control from the “emergency” to the “normal” position to supply air to the trailer brake system.
  • Wait until the air pressure is normal.
  • Check brake system for crossed air lines.
    • Shut off engine so you can hear the brakes.
    • Apply and release trailer brakes and listen for sound of trailer brakes being applied and released. You should hear the brakes move when applied and air escape when the brakes are released.
    • Check air brake system pressure gauge for signs of major air loss.
  • When you are sure trailer brakes are working, start engine.
  • Make sure air pressure is up to normal
The "Fifth Wheel" is the plate and locking mechanism on the tractor which the trailer rest on and locks into.
Remember: Never back up to a trailer on an angle.

Combination Vehicle:

A vehicle with two separate parts - the power unit (tractor) and the trailer. Tractor-trailers are considered combination vehicles.

OWI:

Operating While Intoxicated

Review Questions - Click On The Picture To Begin...

Before coupling a tractor to a trailer, the Fifth Wheel should:
  • Be put in the manual lock position
  • Be free of oil and grease
  • Have the jaws closed
  • Be tilted down towards the rear of the tractor

Quote From The CDL Manual:

Inspect Fifth Wheel Check for damaged/missing parts.

  • Check to see that mounting to tractor is secure, no cracks in frame, etc.
  • Be sure that the fifth wheel plate is greased as required. Failure to keep the fifth wheel plate lubricated could cause steering problems because of friction between the tractor and trailer.
  • Check if fifth wheel is in proper position for coupling:
    • Wheel tilted down towards rear of tractor.
    • Jaws open.
    • Safety unlocking handle in the automatic lock position.
  • If you have a sliding fifth wheel, make sure it is locked.
  • Make sure the trailer kingpin is not bent or broken.
Next
What might happen if the trailer is too high when you try to couple?
  • The fifth wheel plate will automatically adjust to the trailer height
  • Modern trucks are installed with a "trailer height icon" which will illuminate on your dashboard
  • The trailer will be forced downward into the fifth wheel plate, causing damage to the ground or landing gear
  • It may not couple correctly

Quote From The CDL Manual:

Check 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. (If the trailer is too low, the tractor may strike and damage the nose of the trailer; if the trailer is too high, it may not couple correctly.)
  • Check that the kingpin and fifth wheel are aligned.

TruckingTruth's Advice:

In addition to incorrect coupling, if a trailer is too high off the ground and you try to back into it, you may cause damage as the rear of your truck cab could strike the front of the trailer. Further, the trailer king pin may become stuck in front of the fifth wheel plate which can be a costly and time wasting error. Before backing under any trailer, it's very important to visually check the trailer height in relation to your tractors fifth wheel.

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Next
What will happen if the trailer is too low to back under with your truck?
  • Trailers have an "angle plate" which will automatically lift the trailer to the correct height
  • You may strike and damage the nose of the trailer
  • Modern trailers are equipped with "safety bumpers" which will prevent damage from occurring
  • None of these answers are correct

Quote From The CDL Manual:

Check 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. (If the trailer is too low, the tractor may strike and damage the nose of the trailer; if the trailer is too high, it may not couple correctly.)
  • Check that the kingpin and fifth wheel are aligned.
Prev
Next
How should you position your tractor before backing under and connecting to a trailer?
  • Back the tractor to the trailer on the left side
  • Back the tractor to the trailer on the right side
  • Back the tractor directly in front of the trailer
  • Back the tractor to the trailer at a 45 degree angle on either the left or right side

Quote From The CDL Manual:

  • Put the tractor directly in front of the trailer. (Never back under the trailer at an angle because you might push the trailer sideways and break the landing gear.)
  • Check position, using outside mirrors, by looking down both sides of the trailer.

TruckingTruth's Advice:

It will take some practice, but always back under a trailer as straight as possible to avoid turning the trailer over.

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