Combination Test 3 - Crist CDL's Online Testing Center

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Combination Test 3
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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 emergency and service air lines.

b. The electrical service cable.

c. Nothing, back up and lock the fifth wheel.

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.

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

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.

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.

The hand valve should be used:

a. To test the trailer brakes.

b. Only when the trailer is fully loaded.

c. Only with the foot brake.

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

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.

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.

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.

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