Coupling a Loaded Trailer With a Height Mismatch
You are picking up a loaded 53-foot van trailer at a Missouri distribution center. The tractor is a day cab with a sliding fifth wheel; the trailer's kingpin plate sits about 3 inches higher than the tractor's fifth wheel. The yard has a slight slope toward the dock. The previous driver left the trailer's spring brakes set and the red supply line disconnected, but the blue service line is still connected. It is 28°F, and the glad hands are stiff. The trailer has a fiberglass nose and the tractor has a roof fairing; clearance is tight but acceptable. The trailer ABS lamp is on. You need to couple, complete the connection checks, and move the trailer about 200 yards to the scale. A yard jockey is waiting, and another tractor is parked close on your left. The fifth wheel jaws are open and lightly greased. You have a flashlight and wheel chocks.
1. What is your coupling sequence, and how do you deal with the 3-inch height mismatch and the slope before you back under?
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Set the tractor parking brake and chock the trailer wheels, especially because the yard slopes. Confirm the trailer spring brakes are set. The trailer is too high: if you back under as-is, the fifth wheel may strike the trailer or fail to lift it, and the jaws may not lock around the kingpin. Lower the landing gear until the trailer's kingpin plate is just below the fifth wheel, so the tractor will raise the trailer slightly as you back under. Back slowly and squarely, listen for the fifth wheel to lock, then do a tug test in both directions. After the tug test, visually confirm the jaws are closed around the kingpin and the safety latch is in place. Connect the red supply line and blue service line, check for air leaks, charge the trailer system, and confirm the spring brakes release. Raise the landing gear, pull forward gently, and recheck the coupling before moving to the scale.
2. The blue service line was left connected while the red supply line was disconnected. What problems does that create, and what do you check before moving?
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With the red supply line disconnected, the trailer has no reliable source of supply air. The blue service line alone does not charge the trailer system, so the trailer spring brakes will stay applied and the trailer tanks may be nearly empty. Do not assume the trailer is ready just because one line is connected. Connect the red line, listen for the charge, and check that trailer pressure builds. Inspect both glad hand seals and couplers; a stiff or damaged seal can leak. With the tractor protection valve in normal position, release the tractor parking brake and confirm the trailer spring brakes release. Then apply the service brakes and confirm the trailer brakes apply. Check the electrical cord and trailer ABS lamp. If the trailer will not charge or the brakes will not release, stop and fix the connection rather than dragging the trailer.
3. The trailer ABS lamp stays on after you connect and charge the system. Do you move the 200 yards to the scale? What are your reasoning and checks?
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A steady trailer ABS lamp means the trailer ABS has a fault; it does not by itself prove the service brakes are dead. For a controlled 200-yard move at low speed, you may move only after verifying that the trailer service brakes and spring brakes operate and that air loss is acceptable. Do a stationary brake test: apply the service brakes and confirm the trailer brakes hold, then release and confirm they release. Check for leaks at the glad hands and listen for a purge or leak. Keep speed very low and avoid any situation that requires hard braking or skid control. Report the ABS fault and have it repaired before the unit goes on the highway. If any brake check is uncertain, do not move; an ABS fault plus a brake problem is not a short-yardage risk worth taking.