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Uncoupling Tractor Semi-Trailers

The following steps will help you to uncouple safely.

STEP 1: Position Rig

  • Make sure surface of parking area can support weight of trailer.
  • Have tractor lined up with the trailer (pulling out at an angle can damage landing gear).

STEP 2: Ease Pressure on Locking Jaws

  • Shut off trailer air supply to lock trailer brakes.
  • Ease pressure on fifth wheel locking jaws by backing up gently. (This will help you release the fifth wheel locking lever.)
  • Put on parking brakes while tractor is pushing against the kingpin. (This will hold rig with pressure off the locking jaws.)

STEP 3: Chock Trailer Wheels

  • Chock the trailer wheels if the trailer does not have spring brakes or if you are not sure. (The air could leak out of the trailer air tank, releasing its emergency brakes. Without chocks, the trailer could move.)

STEP 4: Lower the Landing Gear

  • If trailer is empty, lower the landing gear until it makes firm contact with the ground.
  • If trailer is loaded, after the landing gear makes firm contact with the ground, turn crank in low gear a few extra turns. This will lift some weight off the tractor. (Do not lift trailer off the fifth wheel.) This will make it easier to unlatch the fifth wheel and easier to couple next time.

STEP 5: Disconnect Air Lines and Electrical Cable

  • Disconnect air lines from trailer. Connect air line glad hands to dummy couplers at back of cab or couple them together
  • Hang electrical cable with plug down to prevent moisture from entering it.
  • Make sure lines are supported so they will not be damaged while driving the tractor.

STEP 6: Unlock Fifth Wheel

  • Raise release handle lock.
  • Pull the release handle to “open” position.
  • Keep legs and feet clear of the rear tractor wheels to avoid serious injury in case the vehicle moves.

STEP 7: Pull Tractor Partially Clear of Trailer

  • Pull tractor forward until fifth wheel comes out from under the trailer.
  • Stop with tractor frame under trailer (prevents trailer from falling to ground if landing gear should collapse or sink).

STEP 8: Secure Tractor

  • Apply parking brake.
  • Place transmission in neutral.

STEP 9: Inspect Trailer Supports

  • Make sure ground is supporting trailer.
  • Make sure landing gear is not damaged.

STEP 10: Pull Tractor Clear of Trailer

  • Release parking brakes.
  • Check the area and drive tractor forward until it clears.

Test Your Knowledge

  1. What might happen if the trailer is too high when you try to couple?
  2. After coupling, how much space should be between the upper and lower fifth wheel?
  3. You should look into the back of the fifth wheel to see if it is locked onto the kingpin. True or False?
  4. To drive you need to raise the landing gear only until it just lifts off the pavement. True or False?

Study section 6.3 if you can't answer all of these questions.

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

When disconnecting from a trailer, you should:
  • The positioning of the tractor is not important as you can disconnect from any angle
  • Put the tractor at a 90 degree angle to the trailer (or as close to 90 degrees as possible)
  • Have the tractor at a 45 degree angle to the left or right of the trailer
  • Have the tractor lined up with the trailer

Quote From The CDL Manual:

Position Rig

  • Make sure surface of parking area can support weight of trailer.
  • Have tractor lined up with the trailer. (Pulling out at an angle can damage landing gear.)
Next
Before disconnecting from a trailer, you should:
  • Set the tractor parking brakes but wait to set the trailer spring brakes until the landing gear has been lowered and the air lines have been disconnected
  • Apply the trailer spring brakes, then back up gently towards the trailer to ease tension off the fifth wheel locking lever
  • Set the trailer spring brakes but wait to set the tractor parking brakes until the landing gear has been lowered and the air lines have been disconnected
  • Apply the trailer spring brakes, then gently pull forward against the trailer to apply tension onto the fifth wheel locking lever

Quote From The CDL Manual:

Ease Pressure on Locking Jaws

  • Shut off trailer air supply to lock trailer brakes.
  • Ease pressure on fifth wheel locking jaws by backing up gently. (This will help you release the fifth wheel locking lever.)
  • Put on parking brakes while tractor is pushing against the kingpin. (This will hold rig with pressure off the locking jaws.
Prev
Next
When dropping an empty trailer, you should lower the landing gear until:
  • The landing gear is 1 to 3 inches above the ground
  • It makes firm contact with the ground
  • You can't turn the landing gear handle any further
  • None of these answers are correct

Quote From The CDL Manual:

Lower the Landing Gear

  • If trailer is empty, lower the landing gear until it makes firm contact with the ground.
  • If trailer is loaded, after the landing gear makes firm contact with the ground, turn crank in low gear a few extra turns. This will lift some weight off the tractor. (Do not lift trailer off the fifth wheel.) This will make it easier to unlatch the fifth wheel and easier to couple next time.
Prev
Finish
Please select an option
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