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CDL · Coupling and Uncoupling

When uncoupling a converter dolly, what is the safe sequence?

Correct answer

Lower the dolly's landing gear; disconnect air and electrical lines; release the pintle hook; pull the tractor and front trailer away, leaving the dolly attached to the second trailer until the dolly is uncoupled separately

  1. A Disconnect at random
  2. B Lower the dolly's landing gear; disconnect air and electrical lines; release the pintle hook; pull the tractor and front trailer away, leaving the dolly attached to the second trailer until the dolly is uncoupled separately
  3. C Always disconnect the second trailer first
  4. D Just pull away when ready

Why this is the answer

Uncoupling a doubles combination requires a specific sequence to prevent dropping a trailer or having a rolling dolly. Standard sequence: (1) park the combination on level ground with brakes set; (2) lower the converter dolly's landing gear until firmly on the ground (then crank a few more turns to take weight off); (3) disconnect the air and electrical lines between the lead trailer and the dolly; (4) release the pintle hook on the lead trailer; (5) pull the tractor and lead trailer forward, leaving the dolly connected to the second trailer; (6) then uncouple the second trailer from the dolly's fifth wheel as a separate operation. Skipping the landing gear step before disconnecting causes drop-offs.
Source: FMCSA CDL Manual 7.2.3 Doubles Uncoupling

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