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CDL · Coupling and Uncoupling

In what order should you uncouple a set of doubles to do it safely?

Reviewed by Jordan Morley, Editorial Lead at 247SimpleTests. Written by the 247SimpleTests Editorial Team from the official source material cited on every question.

Correct answer

Uncouple the rear trailer first — secure it, disconnect the dolly from it, then pull the dolly clear — working from the back of the combination forward

  1. A Uncouple the front trailer first
  2. B Order does not matter for uncoupling
  3. C Uncouple the rear trailer first — secure it, disconnect the dolly from it, then pull the dolly clear — working from the back of the combination forward
  4. D Disconnect all trailers at once

Why this is the answer

Doubles are uncoupled from the rear forward. The driver first secures the rear trailer (lower its landing gear and chock or brake it), then disconnects the air and electric lines and unlocks the dolly's fifth wheel to free the rear trailer. Next the converter dolly is uncoupled from the trailer ahead of it: secure the dolly, release the pintle hook and safety chains, and pull the dolly out. Working back to front keeps each trailer supported and prevents a trailer from rolling or dropping. Rushing or doing it out of order risks dropping a trailer or having the dolly roll free, which can cause injury or damage.
Source: FMCSA CDL Manual 7.2.3 Uncoupling Doubles

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About this topic: Coupling and Uncoupling

Coupling and uncoupling doubles and triples adds the converter dolly and the pintle hook to the usual fifth-wheel procedure, and the order matters — heaviest trailer first, lightest last. These questions walk through the steps and the checks that confirm a secure connection. This is one of 16 Doubles and Triples questions on coupling and uncoupling, each with a full explanation on a single study page.

New to this exam? Our CDL exam guide explains the format, scoring, and how to prepare.

Related questions

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What is a 'converter dolly' in a doubles combination?

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Before coupling a converter dolly to the rear of the first trailer, you should:

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

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When inspecting the pintle hook on a converter dolly before coupling, what should you verify?

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