Coupling and Uncoupling Flashcards

During the coupling process, what is the immediate danger if the trailer is too high when the driver backs the tractor under it?

Answer: The kingpin may travel over the top of the fifth wheel, resulting in a 'high hook'.

A 'high hook' occurs when the trailer is too high, causing the kingpin to slide over, instead of into, the fifth wheel locking mechanism. This is a dangerous situation that can damage the equipment and result in an insecure connection.

A driver is uncoupling a semi-trailer on what appears to be a solid asphalt surface on a hot day. Which of the following is a critical extra step to ensure the trailer remains stable after uncoupling?

Answer: Placing boards or pads under the landing gear.

Hot asphalt can be soft, and the weight of a loaded trailer can cause the landing gear to sink into the surface, potentially making the trailer unstable. Placing boards or pads underneath distributes the weight over a larger area to prevent sinking.

What is the primary purpose of performing a 'tug test' after coupling?

Answer: To ensure the fifth wheel's locking jaws have securely engaged the trailer's kingpin.

The tug test is a physical check to confirm a secure mechanical connection. By setting the trailer brakes and gently pulling the tractor forward, the driver verifies that the fifth wheel has locked onto the kingpin and the trailer will not separate from the tractor.

Which of the following describes the correct procedure for connecting the air lines to a trailer?

Answer: Connect the air lines (glad hands) by pressing them together and rotating them to a 90-degree angle to lock them in place.

Glad hands are connected by aligning the seals, pressing them together, and rotating them approximately 90 degrees until they lock. While the order of connection can vary, the physical action of securing the glad hands is a universal and critical step.

After successfully coupling, the driver raises the landing gear and performs a final visual inspection. What specific detail must the driver confirm by looking at the fifth wheel connection?

Answer: There is no space between the tractor's fifth wheel and the trailer apron, and the locking jaws are closed around the kingpin's shank.

A secure coupling means the trailer's apron is resting flat on the fifth wheel with no gap. The locking jaws must be closed around the base (shank) of the kingpin, not on its head. A gap indicates a potential high hook or failed coupling.

During uncoupling, after chocking the trailer wheels and lowering the landing gear, what is the correct sequence of the next major steps?

Answer: Disconnect air/electrical lines, pull the fifth wheel release, then pull the tractor partially clear of the trailer.

The correct and safe procedure is to first disconnect the lines that connect the tractor and trailer systems. Then, unlock the mechanical connection (the fifth wheel). Finally, slowly pull the tractor forward, stopping when the frame is still under the trailer to double-check stability before pulling completely clear.