TheoryCDL Doubles Triples Practice Questions
Free CDL Doubles Triples practice questions with answers and plain-English explanations. Browse the PDF, video and online mock test.
CDL Doubles Triples Questions
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Q1You are about to couple a second trailer to a loaded converter dolly. The dolly's pintle hook closes but you notice the latch does not fully seat. What is the correct action?
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✓ Correct answer: Do not couple the trailer; the pintle hook latch must be fully closed and locked before any movement
The CDL manual states that all coupling devices must be fully engaged and locked before moving; a pintle hook that does not fully latch is a defect that prohibits operation regardless of safety chain status.
Q2Before coupling a converter dolly to the rear of a first trailer, the dolly landing gear should be:
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✓ Correct answer: Adjusted so the dolly fifth wheel is slightly lower than the trailer's rear kingpin height
The CDL manual specifies that the converter dolly's fifth wheel should be positioned slightly below the kingpin height of the trailer being coupled so the trailer rides up onto the fifth wheel as it is pulled into position, ensuring full engagement.
Q3A driver is assembling a triple-trailer combination. After coupling the second trailer, when should the third trailer's brakes be released for the first time during assembly?
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✓ Correct answer: Only after all air lines are connected, the trailer glad hands are charged, and the combination has been test-pulled forward to check coupling
Per the CDL manual coupling procedure, air lines must be connected and the system charged before brakes are released; and coupling should be verified with a test pull before the trailer's parking brakes are released for road movement.
Q4A driver is performing a coupling inspection and finds that the converter dolly's fifth wheel locking jaws have closed around the kingpin but a gap exists between the fifth wheel plate and the trailer apron plate. What does this indicate?
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✓ Correct answer: The kingpin may not be fully seated; the trailer may be resting on the fifth wheel lip rather than the plate surface
The CDL manual states there should be no gap between the upper fifth wheel plate and the trailer apron plate after coupling; a visible gap means the kingpin has not dropped fully into the jaws and the coupling is incomplete.
Q5After coupling the converter dolly to the rear of the first trailer using a pintle hook, what immediate check must the driver perform before backing under the second trailer?
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✓ Correct answer: Verify that the pintle hook is locked and the safety chains are connected
The CDL manual requires the driver to verify that the pintle hook latch is secured and locked and that safety chains are properly connected before any movement toward the next trailer in the combination.
Q6When building a doubles combination on a grade (slope), what additional step must be taken before uncoupling the tractor from the first trailer?
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✓ Correct answer: Chock all trailer wheels to prevent rolling before the tractor brakes are released
The CDL manual specifies that wheel chocks must be used on any grade before uncoupling because trailer parking brakes alone may not reliably hold a loaded trailer on a slope.
Q7A converter dolly has two axles and a single pintle hook eye. When you connect this dolly's air lines to the first trailer, which glad hand connection controls the dolly's spring brakes?
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✓ Correct answer: The emergency (supply) glad hand, which charges the dolly's air tanks and releases the spring brakes when connected
Per the CDL manual, the emergency (supply) line glad hand charges the converter dolly's air reservoir and releases the spring parking brakes; disconnecting the supply line causes the dolly's spring brakes to apply automatically.
Q8During assembly of a doubles combination, you must move the converter dolly from a parked position to the rear of the first trailer. Which is the safest method according to CDL manual guidelines?
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✓ Correct answer: Hand-push the converter dolly into position after releasing its parking brakes
The CDL manual instructs the driver to release the converter dolly's brakes and hand-push it into position when the terrain allows, avoiding the hazards of improvised towing connections that could fail.
Q9You have just coupled the second trailer in a doubles set and connected all air lines. The trailer air supply gauge shows a pressure drop that stabilizes at 85 psi instead of climbing to normal operating pressure. What is the most likely cause and correct action?
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✓ Correct answer: A likely air leak at one of the glad hand connections or trailer air lines; inspect and repair before moving
The CDL manual instructs drivers to check for air leaks after coupling by monitoring pressure gauges; a pressure reading that stabilizes below normal operating pressure rather than building indicates a leak that must be found and corrected before driving.
Q10What is the purpose of the converter dolly's safety chains when connecting it to a second trailer?
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✓ Correct answer: To keep the dolly connected to the trailer if the pintle hook or kingpin coupling fails
Per the CDL manual, safety chains provide a secondary connection between the converter dolly and the trailer so that if the primary coupling device (pintle hook or fifth wheel) fails, the trailer remains attached to the combination.
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