CDL Combination Vehicles Practice Test 3

Question 1

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

Accepted Answer

Pulling the tractor forward gently with the trailer brakes locked

Answer

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

Question 2

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

Accepted Answer

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

Answer

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

Question 3

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

Accepted Answer

Emergency (spring) brakes

Answer

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

Question 4

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

Accepted Answer

There should be no space between them

Answer

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

Question 5

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

Accepted Answer

A sudden steering move amplifying trailer sway and risking rollover

Answer

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

CDL Practice Test