Coupling & Uncoupling
10 free questions, part of the Doubles/Triples (T) Endorsement CDL practice test
ELDT.io's coupling and uncoupling bank has 10 free practice questions covering how to couple and uncouple converter dollies on twin and triple trailer combinations. Every question is built from 49 CFR 383.115(a), the federal section on assembly and hookup procedures for combination vehicles. Expect questions on pintle hook sequencing, landing gear positioning, and the correct order of operations for building or breaking down a full triples rig.
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What is a converter dolly?
A converter dolly is the axle-and-frame unit with its own fifth wheel that connects a second or third trailer to the unit in front of it. It attaches to the lead trailer with a pintle hook or similar drawbar connection, and the next trailer mounts on its fifth wheel the same way a trailer mounts on a tractor.
Why can't you unlock a converter dolly's pintle hook while it's still under the rear trailer?
Doing so lets the dolly roll free while the trailer's full weight is still resting on it, which can cause the dolly to shoot out or the trailer to drop suddenly. The rear trailer has to be supported on its own landing gear before you touch the pintle hook.
What's the correct order for coupling a full triples rig?
Couple the tractor to the first trailer, then attach a converter dolly to that trailer, couple the second trailer to the dolly, attach a second dolly, and couple the third trailer last. Each connection gets checked for a secure lock before you move to the next one.
How do you confirm a converter dolly coupling is secure before hooking up air and electrical lines?
Back under the rear trailer, raise the landing gear slightly to put weight on the dolly's fifth wheel, then pull forward gently against the trailer to confirm the jaws have locked around the kingpin before connecting any lines.
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