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CDL · Coupling and Uncoupling

After coupling, how should a driver verify the fifth wheel is properly locked onto the kingpin?

Correct answer

Visually inspect from underneath/the side with a flashlight to confirm the locking jaws have closed around the kingpin shank (not the head), there is no gap between the trailer and fifth wheel, and the locking lever/handle is in the locked position — plus perform a tug test

  1. A Just look at it from the driver's seat
  2. B Visually inspect from underneath/the side with a flashlight to confirm the locking jaws have closed around the kingpin shank (not the head), there is no gap between the trailer and fifth wheel, and the locking lever/handle is in the locked position — plus perform a tug test
  3. C Honk the horn twice
  4. D Drive forward at high speed to test

Why this is the answer

VERIFYING THE COUPLING: After backing under, verify the connection by: (1) TUG TEST: With the trailer brakes locked, gently pull forward against the kingpin — the tractor and trailer should not separate; (2) VISUAL INSPECTION: Get out and look under the trailer with a flashlight; confirm the LOCKING JAWS have closed completely around the kingpin SHANK (the narrow part), NOT just resting on the kingpin head; confirm there is NO GAP between the trailer apron and the fifth wheel (a gap indicates a high hitch); confirm the locking lever/handle is in the LOCKED position and the safety latch (if equipped) is engaged; THE DANGER — HIGH HITCH: When the fifth wheel jaws close in front of or on top of the kingpin head rather than around the shank — it may hold briefly then release, dropping the trailer; ALWAYS do both the tug test AND a visual inspection — never rely on sound or feel alone; this verification is critical to prevent trailer separation.
Source: FMCSA CDL Manual — Coupling Verification

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