Converter Dollies and Fifth Wheel Connections
Converter Dollies and Fifth Wheel Connections
A converter dolly is the short axle assembly that links a second trailer to the rear of the first. It carries a fifth wheel for the second trailer's kingpin, a pintle hook or drawbar for attachment to the first trailer, air lines, electrical cord, and safety chains. The exam tests inspection and connection order.
Dolly inspection
- Check the pintle hook for wear, the latch for positive closure, and the safety chains for cracks.
- Inspect the dolly fifth wheel for cracked jaws, missing bolts, and lubrication.
- Check tires, rims, mud flaps, lights, and the dolly's own brakes.
- Confirm gladhands and seals are clean and the lines are long enough to turn without stretching.
Connection order
- Chock the dolly wheels and set its spring brakes.
- Back the tractor/first trailer to the dolly; latch the pintle and cross the safety chains.
- Connect the service and emergency air lines and the electrical cord.
- Back the second trailer onto the dolly fifth wheel; tug-test; connect lines.
- Release the dolly spring brakes only after all connections are complete.
Worked example
A driver connects the dolly air lines but leaves the dolly spring brakes set. The combination will not roll freely and the dolly tires drag. The driver must release the dolly parking brakes after the lines are charged. Conversely, releasing them before connection lets the dolly roll away.
Traps
- Connecting the second trailer before the dolly is secured to the first.
- Forgetting the safety chains.
- Crossed gladhands: service line to emergency coupler.
- A fifth wheel jaw that is not locked; always tug-test.