CDL Combination Vehicles Test 3 – Classic Mode

This is CDL Combination Vehicles Test 3 in our original Classic Mode. Simply click in your answer to each CDL practice test question. When you're finished, check your score and results. You can reset the test and retake it as needed.


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1. You should not back a tractor under a trailer until the whole air system is:

A Between 60 and 80 psi
B Empty.
C Bled down to half the maximum pressure
D At normal pressure

2. You are coupling a semi trailer to your tractor but have not yet backed under. The trailer is at the right height when:

A It will be raised slightly when the tractor is backed under it.
B The kingpin is about 1 1/4 inches above the fifth wheel.
C The end of the kingpin is even with the top of the fifth wheel.
D The fifth wheel is sure to miss the kingpin.

3. Which part of the kingpin should the locking jaws close around?

A The base
B The shank
C The shiny section
D The head


4. When you get ready to back under the semi trailer you should line up:

A About 12 degrees off the line of the trailer.
B The kingpin to engage the driver's side locking jaw first.
C Exactly one trailer length in back of the trailer.
D Directly in front of the trailer.

5. How should you test the tractor semi trailer connection for security?

A Pull gently forward in low gear against the locked trailer brakes, then look at it carefully.
B Put the tractor in gear and pull ahead with a sharp jerk.
C Rock the trailer back and forth with the trailer brakes locked.
D Don't worry. The connection should be fine.

6. When should you use the hand valve to park a combination vehicle?

A To park at loading docks.
B Never
C To park on a grade
D In sub-freezing temperatures.

7. You supply air to the trailer tanks by:

A Pushing in the trailer air supply valve.
B Pulling out the trailer air supply valve.
C Connecting the blue line to the red line.
D Connecting the service line glad hand.

8. Why should you be sure that the fifth wheel plate is greased as required?

A To reduce heat and noise
B To prevent steering problems
C To ensure good electrical connections
D To make uncoupling easier.

9. After you supply air to the trailer, make sure the air lines are not crossed and the trailer brakes are working. This is done by:

A Applying and releasing the trailer brakes and listening for brake sounds.
B Lifting the brake pedal.
C Turning on the parking brakes from the cab.
D Releasing the tractor brakes.

10. There are two things that a driver can do to prevent a roll over. They are: (1) Keep the cargo as close to the ground as possible; and (2):

A Make sure that the brakes are properly adjusted.
B Keep the fifth wheel's free play as tight as possible.
C Go slowly around turns.
D Never drive a tanker.

End of Test #3

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