CDL (Commercial Driver's License) Practice Test (Combination Vehicles #2)


Welcome future truck drivers! The following is the CDL Combination Vehicles Practice Test #2. Simply click in your answer (A,B,C, or D) to each CDL practice test question. When you're done, check your score and the results. You can reset the test and retake it as many times as you want.

CDL Combination Vehicles Practice Test #2

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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.

11. 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.

12. 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.

13. 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

14. 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.

15. 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.

16. Why should you lock the tractor glad hands (or dummy couplers) to each other when you are not towing a trailer?

A The connected brake circuit becomes a back up air tank.
B If you did not, you could never build system pressure.
C It will keep dirt and water out of the lines.
D You should never do this.

17. The safety catch for the fifth wheel locking lever must be ____ for a coupling to be complete.

A Under the locking lever
B Over the locking lever
C Through the locking lever
D Inside the locking lever

18. The front trailer supports are up and the trailer is resting on the tractor. Make sure:

A There is enough clearance between the tractor frame and the landing gear.
B There is enough clearance between the tops of the tractor tires and the nose of the trailer.
C Both a and b are correct.
D None of the above.

19. You have a major leak in the service line and you put on the brakes. Service air pressure will escape and cause the:

A Trailer tank pressure to be lost.
B Trailer emergency brakes to come on.
C Tractor spring brakes to lock on.
D None of the above.

20. When backing under a tractor under a trailer you should expect:

A Trailer will be lifted slightly when the tractor backs under it.
B End of the kingpin is even with the top of the fifth wheel.
C Trailer landing gear is fully extended.
D No movement of the trailer if you've done it correctly.

21. You are coupling a tractor to a semi trailer and have backed up but are not under it. What should you hook up before backing under?

A The safety chain.
B The electrical service cable.
C Nothing, back up and lock the fifth wheel.
D The emergency and service air lines.

22. You have coupled with a semi trailer. In what position should you put the front trailer supports before driving away?

A Three turns off the top with the crank handle secured in it?s bracket.
B Fully raised with the crank handle secured in its bracket.
C Raised 1/2 way with the crank handle removed.
D None of the above.

23. Air lines on a combination vehicle are often colored to keep them from getting mixed up. The emergency line is ____; the service line is ____.

A Red, blue
B Blue, red
C Black, yellow
D Depends on the type of trailer

24. Which of these statements is true?

A Light vehicles need more braking power to stop than heavy ones.
B Always delay braking a heavy vehicle until you have no other choice.
C "Bobtail" tractors can take longer to stop than a combination vehicle loaded to the maximum gross weight.
D None of the above.

25. You are coupling a tractor and semi trailer and have connected the air lines. Before backing under the trailer, you should:

A Make sure that the trailer brakes are off.
B Supply air to the trailer system, then pull out the air supply knob to lock the trailer brakes.
C Apply the brakes twice to alert others.
D All of the above.

26. 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.

27. 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

28. 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.

29. 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.

30. 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.

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