Combination Vehicles Practice Test Flashcards

After coupling, you should check that the fifth wheel is locked by:

Answer: Pulling the tractor forward gently with the trailer brakes locked

With the trailer brakes locked, gently pulling forward against the kingpin (tug test) confirms the fifth wheel is firmly locked.

What is the proper height for the fifth wheel before backing under the trailer?

Answer: The trailer will be raised slightly when the tractor backs under it

The fifth wheel should be low enough that the tractor raises the trailer slightly as it backs under, ensuring solid contact.

Trailer brakes that come on automatically when the air supply is lost are called:

Answer: Emergency (spring) brakes

Spring brakes apply automatically when air pressure drops, providing an emergency braking function.

When checking the coupling, the gap between the upper and lower fifth wheel should be:

Answer: There should be no space between them

There should be no space between the upper and lower fifth wheel; a gap means something is wrong and could cause separation.

The 'crack-the-whip' effect in combination vehicles refers to:

Answer: A sudden steering move amplifying trailer sway and risking rollover

Quick steering movements can throw the trailer sideways, and this rearward amplification can cause the trailer to roll over.

Glad hands are used to:

Answer: Connect the service and emergency air lines between tractor and trailer

Glad hands are the coupling devices used to connect the air brake lines between the tractor and trailer.

If the service air line connection is crossed with the emergency line, what may happen?

Answer: You may not have trailer service brakes when you press the brake pedal

Crossed air lines can leave you without trailer service braking, a dangerous condition you must check for before driving.