Coupling a Converter Dolly on a Sloped Yard
At a Detroit-area terminal, you are building a set of doubles. The tractor is already coupled to the first 28-foot trailer, which is parked on a paved yard with a 2–3% slope toward a chain-link fence. The converter dolly is chocked, its spring brakes are set because it has no air supply, and its fifth wheel is 1 inch lower than the second trailer's kingpin plate. The second trailer's landing gear is down and its brakes are released. You have a fifth-wheel puller bar, wheel chocks, and a supply of gladhand seals. The yard is tight: you must back the dolly under the second trailer without pushing it backward more than a few inches. A spotter is available but is new and has never coupled a dolly. Your appointment slot is in 20 minutes, and the dispatcher wants you to 'just hook and go.' What do you do?
1. What sequence will you use to couple the dolly to the second trailer, and how will you handle the dolly's set spring brakes and the slope?
Read the worked answer
First, I would stop and not let the dispatcher rush me. I would confirm the first trailer's spring brakes are set, chock the second trailer's wheels, and check that the second trailer's kingpin and upper coupler are at the right height for the dolly fifth wheel. Because the dolly has no air, I would connect its emergency (blue) line to the first trailer's rear supply gladhand-or use shop air if the dolly is not yet attached-to charge the dolly, then release its spring brakes only after the wheels are chocked and the tractor is positioned. I would back under squarely in low gear, with the spotter at the rear corner giving hand signals. Once the jaws close, I would do a pull test, verify the locking jaws and safety latch, then connect the service line, electrical cord, and safety chains. I would not raise the second trailer's landing gear until the coupling is proven. On the slope, the chocks stay until the pull test passes. If the dolly rolls or the trailer creeps, I stop and reset.
2. After the jaws close, the puller bar will not move and you see a 1/4-inch gap between the dolly's fifth wheel and the trailer's upper coupler. The spotter says it is close enough. What do you do?
Read the worked answer
A 1/4-inch gap is not 'close enough.' It suggests the kingpin is not fully seated in the jaws or the fifth wheel is too low or too high. I would not move the combination. I would check the fifth-wheel height, the kingpin, the jaw position, and the release handle; then pull forward, reset the fifth wheel, and recouple. I would repeat the tug test and visually confirm the jaws are closed around the kingpin with the safety latch engaged. If the jaws will not lock or the gap remains, I would red-tag the dolly and get maintenance. Forcing the puller bar or moving with a gap risks a dropped trailer.
3. If the second trailer starts to roll backward while you are backing the dolly under it, what is your immediate action, and what would make you refuse the load?
Read the worked answer
If the second trailer starts to roll backward, I would stop backing immediately, hold the brakes, set the trailer spring brakes, and chock the wheels. I would not chase the trailer or put myself between the trailer and the dolly. Then I would inspect the kingpin, landing gear, and brakes for damage and reset the position on level ground if possible. I would refuse the load if the trailer brakes will not hold, the kingpin or upper coupler is damaged, the landing gear is bent, or the slope cannot be controlled with chocks and brakes. A 2–3% slope is enough to move a trailer once the brakes are released.