Coupling on a 2 Percent Grade
After a pump test, the tractor and trailer have been separated for 40 minutes. The rig is on a concrete apron with a 2 percent grade, sloping toward the rear of the trailer. The trailer landing gear is down, wheels chocked on the left side only, and the trailer spring brakes are set. The driver backs the tractor to the trailer. The tiller operator is positioned at the left rear of the tractor. The fifth wheel jaw is open, the kingpin is greased, and the air lines are lying on the ground. The driver says he has coupled many times and asks the tiller operator to just connect the lines. The tractor's fifth wheel height was set for a different trailer earlier in the day, and no one has checked it since.
1. What must the tiller operator verify before the tractor is backed under the trailer, given the grade and chocking?
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Before any movement, the trailer must be secured against the grade. Only the left side is chocked, and the apron slopes toward the rear of the trailer, so the trailer could move backward or pivot if the spring brakes are released or fail. Both sides should be chocked, with fore-and-aft blocking on the downhill side. The trailer spring brakes should be set and confirmed.
The tiller operator should also check the kingpin for damage and lubrication, confirm the fifth wheel jaw is open, and verify the fifth wheel height matches the trailer. The height was set for a different trailer, so the tractor could strike the landing gear or fail to pick up the trailer properly. Landing gear height and clearance must be checked before backing. All personnel should be clear of the gap between the tractor and trailer. The tiller operator should take a position at the left rear of the tractor where the driver can see them and where they can see the gap, then signal the driver to back slowly and stop before contact.
2. After the tractor is under the trailer, what sequence confirms a positive coupling before the landing gear is raised?
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First, make a visual check: the fifth wheel jaw must be closed around the kingpin and the release handle must be fully in the locked position. Second, perform a tug test with the trailer brakes set and the tractor parking brake applied. The driver pulls forward gently against the trailer; if the tractor moves and the trailer does not, the coupling is suspect and must be inspected before continuing. Do not rely on the sound of the coupling alone.
Third, connect the air lines and electrical cord, charge the trailer air system, and test the trailer brakes and lights. Fourth, raise the landing gear only after the coupling and brake tests pass. The tiller operator should confirm each step by voice or hand signal and stay clear of the landing gear and the gap. On this grade, keep the chocks in place until the combination is fully coupled and the brakes have been tested. If any step fails, stop and correct it before raising the landing gear.
3. What is wrong with the current chocking, and how should uncoupling be performed on this grade?
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Only the left side is chocked, and the grade slopes toward the rear of the trailer. That allows the trailer to move laterally or backward if the spring brakes are released or if the surface is slick. Both sides should be chocked, with blocking that prevents fore-and-aft movement.
For uncoupling, the preferred approach is to move to firm, level ground. If that is not possible, chock all wheels, set the trailer spring brakes, lower the landing gear to firm ground, and take the load off the fifth wheel. Disconnect the air lines and electrical cord, then release the fifth wheel jaw and pull the tractor straight forward slowly. The tiller operator should watch the gap and the landing gear and keep personnel clear. Never uncouple with the trailer brakes released, with only one side chocked, or with the landing gear on soft ground that cannot carry the trailer's weight.