Coupling and Uncoupling
Coupling and Uncoupling tests the sequence and the proof. The exam rewards exact order and the checks that prove a coupling actually happened, and it punishes the shortcuts that drop trailers on the road.
Coupling, in order
- Inspect the fifth wheel: jaws open, plate greased, mounting bolts tight, release handle secured by its safety latch.
- Check the kingpin and trailer apron for damage. Chock the trailer wheels.
- Back under slowly and squarely, at the right height, until the fifth wheel contacts the apron.
- Watch and listen for the jaws closing. Then look: jaws closed around the kingpin, safety latch over the release handle, trailer flat on the fifth wheel.
- Tug test. With the trailer spring brakes set, pull forward gently against them. If the coupling is bad, the tractor slides out and the trailer stays put.
- Connect the lines: red to red, blue to blue, then the electrical cord. Leave enough slack for turns, with no chafing.
- Charge the trailer, confirm the trailer brakes release and reapply, and check the trailer lights from the cab.
- Raise the landing gear fully and secure the crank handle. Remove the chocks.
Uncoupling, in order
Park on firm, level ground; set the parking brake; chock the wheels. Lower the landing gear to the ground and give it a few extra turns to take the weight. Disconnect the electrical cord, then the red emergency line (which sets the trailer spring brakes), then the blue service line. Pull the fifth wheel release handle, secure it, and pull forward slowly.
Worked example
A driver hears the click, hooks up the lines, raises the gear, and drives off. On the first turn the trailer slides off the fifth wheel. The click only means the jaws contacted the kingpin; it does not prove they locked around it. A tug test with the trailer brakes set would have exposed the problem in the yard, at walking speed, instead of on a public road.
Traps
- Raising the landing gear before the tug test.
- Relying on the click and skipping the visual check of the jaws and latch.
- Backing under misaligned, which bends the kingpin or apron.
- Uncoupling before the landing gear carries the trailer's weight.