CDL Combination Vehicles Test 6 – Classic Mode

This is CDL Combination Vehicles Test 6 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. Before you back under a trailer, make sure the:

A Air brakes are off.
B Tractor protection valve is normal.
C Landing gear is up.
D Trailer brakes are locked.

2. If the service air line comes apart while you are driving a combination vehicle but the emergency line stays together, what will happen right away?

A Nothing is likely to happen until you try to apply the brakes.
B You'll come to a complete stop.
C The trailer's air tank will exhaust through the open line.
D The emergency tractor brakes will come on.

3. The air leakage rate for a combination vehicle (engine off, brakes on) should not be more than ____ psi per minute.

A 2
B 3
C 4
D 2 1/2

4. In normal driving, some drivers use the hand valve before applying the brake pedal to prevent a jackknife. Which of these statements is true?

A It results in less skidding than using the brake pedal alone.
B It should not be done.
C It is the best way to brake and keep the truck in a straight line.
D It should only be used if you're aware of the dangers.

5. The driver crosses the air lines when hooking up to an old trailer. What will happen?

A If the trailer has no spring brakes, you can drive away, but you will not have trailer brakes.
B The brake pedal will work the trailer spring brakes instead of the air brakes.
C The hand valve will apply the tractor brakes instead of the trailer brakes.
D None of the above.

6. The hand valve should be used:

A To test the trailer brakes.
B Only when the trailer is fully loaded.
C Only in emergencies.
D Only with the foot brake.

7. The air leakage rate for a combination vehicle (engine off, brakes off) should be no more than ____ psi per minute.

A 1
B 2
C 3
D 4

8. The fifth wheel locking lever is not locked after the jaws close around the kingpin. This means that:

A You can set the fifth wheel for weight balance.
B The coupling is not right and should be fixed before driving the vehicle.
C The parking lock is off and you may drive away.
D The fifth wheel needs to be replaced.

9. You are driving a combination vehicle when the trailer breaks away, pulling apart both air lines. You would expect the trailer brakes to come on and:

A The trailer supply valve to stay open.
B The tractor to lose all air pressure.
C The tractor protection valve to close.
D The tractor protection valve to open.

10. Semi trailers made before 1975 that are equipped with air brakes:

A Often do not have spring brakes.
B Usually need a glad hand converter.
C Are easier to brake because they are heavier.
D Only were equipped with spring brakes.

End of Test #6

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