247SimpleTests
CDL · Coupling and Uncoupling

When uncoupling a doubles combination, in what order should the trailers be disconnected?

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

Disconnect the rear trailer and dolly from the front trailer first; then move the combination to appropriate positions before uncoupling the front trailer from the tractor — this prevents the dolly from swinging free with the rear trailer still attached

  1. A Disconnect the rear trailer and dolly from the front trailer first; then move the combination to appropriate positions before uncoupling the front trailer from the tractor — this prevents the dolly from swinging free with the rear trailer still attached
  2. B Both trailers can be disconnected simultaneously
  3. C Disconnect the front trailer first
  4. D Order does not matter as long as brakes are set

Why this is the answer

UNCOUPLING DOUBLES requires a specific sequence to prevent equipment damage and safety hazards from uncontrolled dolly movement.

Correct sequence for uncoupling a doubles: STEP 1 — Park the combination; set the tractor parking brakes; charge the trailer air supply to set all trailer emergency brakes; STEP 2 — Uncouple the REAR TRAILER from the converter dolly: support the rear trailer's weight by cranking down its landing gear; disconnect the pintle hook; remove safety chains; disconnect air and electrical lines from the rear trailer; STEP 3 — Move the tractor with the first trailer and now-empty dolly to a separate location; STEP 4 — Park the tractor and front trailer; set the dolly's parking brake if equipped; lower the dolly's landing legs; disconnect the dolly from the first trailer's pintle ring and remove it; STEP 5 — Uncouple the tractor from the first semitrailer using standard uncoupling procedure.

Why the order matters: If the dolly is disconnected from the front trailer before the rear trailer is removed from the dolly, the dolly and rear trailer are left as a freestanding unit with no tractor control — the dolly's air brakes will hold them temporarily, but this is an unstable configuration that must be managed carefully.

Source: FMCSA CDL Manual, Chapter 7, Doubles and Triples, Uncoupling Sequence

Practice more questions

This question is from our CDL Practice Tests practice test. Take the full practice test to test your knowledge across all Coupling and Uncoupling and other topics.

Take the Doubles and Triples practice test →

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

Coupling and Uncoupling

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

 Coupling and Uncoupling

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

 Coupling and Uncoupling

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

 Coupling and Uncoupling

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

State-specific guides

Need information for your state? Our state guides cover local requirements, fees, and what to expect on exam day.

California Texas Florida New York Pennsylvania Illinois Ohio Georgia

Recommended study materials

Study guide

CDL Study Guide (Trivium)

Complete prep for all CDL written tests: general knowledge, air brakes, combination vehicles, hazmat, and all endorsements. Includes full-length practice tests.

Check Price → Study guide

CDL Practice Tests & Flashcards (Accepted Inc.)

600+ practice questions covering every FMCSA knowledge area, plus 400 flashcards for endorsement prep.

Check Price → Study guide

Master the CDL Truck Driver's License (Arco)

Arco's classic CDL prep with in-depth FMCSA manual coverage, endorsement chapters, and scored practice exams.

Check Price →

As an Amazon Associate, CJ Affiliate, and AWIN publisher we earn from qualifying purchases. Links above are affiliate links. Full disclosure →