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CDL · General

What is the correct first step when uncoupling a trailer?

Correct answer

Position the rig properly (straight, on level ground), then lower the landing gear until it just touches the ground (and lift slightly to remove some weight from the fifth wheel) before disconnecting

  1. A Pull the fifth wheel release handle immediately
  2. B Position the rig properly (straight, on level ground), then lower the landing gear until it just touches the ground (and lift slightly to remove some weight from the fifth wheel) before disconnecting
  3. C Drive away from the trailer quickly
  4. D Disconnect the air lines first

Why this is the answer

UNCOUPLING PROCEDURE (correct sequence): (1) Position the rig — straight, on level, solid ground; (2) Lower the landing gear until it just touches the ground, then crank a few more turns to lift SOME (not all) weight off the fifth wheel — this makes uncoupling easier and prevents the trailer from dropping suddenly; (3) Set the trailer parking brakes; (4) Disconnect the air lines and electrical line, secure them; (5) Unlock the fifth wheel (pull release handle); (6) Slowly pull the tractor partially clear (so it's still under the trailer for support); (7) Check the trailer is fully supported by the landing gear; (8) Then pull completely clear; KEY POINTS: Don't lower landing gear all the way before removing fifth weight (it should support the trailer after uncoupling); ensure the ground is solid (landing gear can sink into soft ground, dropping the trailer); never pull out from under a trailer that isn't properly supported; improper uncoupling causes dropped trailers and injuries.
Source: FMCSA CDL Manual — Uncoupling Procedure

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