For veteran drivers, unhooking a semi-trailer happens several times a day. For others, it may only be once or twice a week. Yet errors still occur — trailers get dropped on the ground requiring cranes or forklifts, or worse, fall off the back of the truck on the road. The procedure should take less than five minutes, but skipping steps will likely result in a trailer on the ground at some point in your career.
Step-by-Step Uncoupling Procedure
- 1
Ensure the ground will support the trailer weight. Use planking under the landing gear if the surface is soft, gravel, or hot asphalt.
- 2
If equipped with an air suspension dump valve, empty the air suspension.
- 3
Wind down the landing gear until it touches the ground firmly. Stow the crank handle.
- 4
Disconnect air lines and the electrical cord. Stow them in dummy couplers or secure with a bungee cord so they don’t drag.
- 5
Pull the 5th wheel release handle to unlock the jaws. Use a 5th wheel puller if available.
- 6
Move the tractor ahead approximately 6 inches using “bull” or low gear.
- 7
Stop and dump (lower) the tractor’s air ride suspension.
- 8
Move ahead slowly until the trailer slides off the back of the 5th wheel. The trailer should be wholly supported by the landing gear with the truck frame still under the trailer.
- 9
Stop, shift to neutral, and set the parking brake.
- 10
Get out and visually confirm the ground is supporting the trailer’s weight and the trailer is stable.
- 11
Get back in the cab, re-inflate the tractor’s air suspension, and drive clear. Done.
What Could Go Wrong
- •Ground integrity: The trailer could sink if the ground isn’t inspected first. Hot asphalt can be damaged by landing gear — always use boards under dolly pads.
- •Forgetting to dump air suspension on a loaded trailer before disconnecting can cause landing gear damage as air bleeds off over time.
- •Always wind landing gear down first. Forgetting this step and driving away will drop the trailer.
- •Disconnect airlines immediately after landing gear — nothing will make you look more amateur than driving away and snapping off the air lines.
- •Move forward slightly before dumping air suspension to disengage the king pin flange from the 5th wheel jaws.
- •Don’t just pull out and drive away. Pull out only far enough that the trailer comes off the 5th wheel, then stop and verify stability.