Fifth Wheel Wear and Bent Landing Gear Leg
A 2018 53 ft dry van is at a loading dock with the landing gear down. The driver reports that the fifth wheel did not lock positively on the last couple of hookups and that the landing gear crank is very hard to turn. Inspection shows a kingpin with visible wear and a step at the wear area. The fifth wheel jaw-to-kingpin gap is 2.0 mm (0.080 in), and the manufacturer's limit is 0.5 mm (0.020 in). The fifth wheel plate has a worn depression, and the jaw spring is weak. The landing gear has one leg bent about 15 mm over its length, and the crank turns with a binding feel. The trailer is loaded and must be moved off the dock before repair. The kingpin is a weld-in type, and the trailer has a steel upper coupler.
1. Evaluate the fifth wheel and kingpin condition against the measurements. Is the gap alone enough to condemn the fifth wheel, and what else must be checked before deciding on repair or replacement?
Read the worked answer
The 2.0 mm jaw-to-kingpin gap is four times the 0.5 mm limit, so the fifth wheel locking mechanism is worn beyond specification. The gap alone is strong evidence that the jaws, wedge, or adjustment are out of limits, but it is not enough to condemn the entire fifth wheel without checking the kingpin. A worn kingpin with a step can produce an excessive gap even if the jaws are serviceable, and replacing only the jaws would leave a worn kingpin that may not lock securely.
I would measure the kingpin diameter at the wear area and compare with the manufacturer's minimum, inspect for a step or taper, and check the upper coupler plate for cracks and severe wear. I would also inspect the jaw spring, wedge, and adjustment mechanism and verify that the fifth wheel is the correct size for the kingpin. If the kingpin is within limits and the jaws are worn, the fifth wheel can be rebuilt or replaced according to the manufacturer's procedure. If the kingpin is worn or stepped, the kingpin must be replaced as well. The worn plate depression can affect coupling height and should be evaluated against the manufacturer's limits.
2. The trailer must be moved off the dock before repair. What is a safe plan, and what would make you refuse to move it?
Read the worked answer
I would not move the trailer with a known kingpin or fifth wheel locking defect unless I could establish a positive coupling. First, I would determine whether the tractor's fifth wheel is compatible and whether the jaws can be adjusted or the locking mechanism can be verified as fully engaged. I would inspect the coupling from under the trailer after hookup, confirm the jaws are closed around the kingpin, and check that the release handle is fully in and the safety latch is engaged. I would use a tug test and visually confirm the gap. If the kingpin is worn or stepped enough that the jaws cannot lock positively, moving the trailer is unsafe.
I would refuse to move it if the jaws will not close, the handle will not latch, the kingpin is visibly worn or cracked, or the fifth wheel mounting is cracked or loose. In that case, the trailer must be lifted or supported and repaired in place, or moved only with a proper recovery procedure. The bent landing gear also affects the move: the trailer must be supported safely before the gear is repaired, and the gear should not be used to carry the load if the leg is bent and binding.
3. Outline the landing gear repair and the checks needed before the trailer is returned to service. Include how you would handle the loaded condition.
Read the worked answer
Because the trailer is loaded, I would first support the trailer with approved stands or blocks under the frame or landing-gear mounting area, following the manufacturer's lifting points. I would not rely on the bent leg to hold the load while it is being repaired. I would remove the landing gear leg or the gear assembly as required, inspect the mounting brackets and frame for cracks or deformation, and replace the bent leg rather than straightening it unless the manufacturer permits straightening. I would check the crank, gears, cross shaft, and bearings for binding and lubricate them with the specified lubricant.
After assembly, I would lower the trailer onto the gear, confirm both legs carry load evenly, and crank the gear up and down through its full travel. I would check for binding, abnormal noise, and proper foot contact, then inspect the mounting bolts and welds. The fifth wheel repair should be completed and verified before the trailer is coupled and moved. I would document the kingpin and fifth wheel measurements, the replacement parts, and the landing gear repair, and road-test the trailer before returning it to service.