CDL Combination Practice Test
Hook up the emergency and service air lines. - ANS-You're hooking up a tractor to a semi-trailer
and have backed up but are not under it. What should you do before backing under the trailer?
At normal pressure - ANS-After pushing in the trailer supply valve, you should not move the
tractor
until air system is?
Reduce speed before entering turns. - ANS-There are two things you can do to prevent a
rollover. They are: Keep the cargo as close to the ground as possible, and:
3 psi - ANS-With the engine off and the brakes released, a combination vehicle air brake system
shouldn't leak more than how many psi in one minute?
The coupling is not correct and should be corrected before driving the coupled unit. - ANS-The
fifth wheel locking lever isn't locked after the jaws close around the kingpin. This means that:
If the trailer has no spring brakes, you could drive away, but you wouldn't have trailer brakes. -
ANS-You cross the air lines when hooking up to an old trailer. What will happen?
Fully raised with the crank handle secured - ANS-How far should you crank up the front trailer
supports after coupling a semi-trailer?
Usually do not have spring brakes - ANS-Air brake equipped trailers made before 1975
Never - ANS-The hand valve should be used to park a combination vehicle:
Red - ANS-Air lines on a combination vehicle are often colored to keep them from getting mixed
up. The emergency line is ____
By pushing in the trailer air supply valve. - ANS-How do you supply air to the air tank on the
trailer?
It should never be done. - ANS-In normal driving, some drivers use the hand valve before
applying the brake pedal to prevent trailer skids. Which of these statements is true?
Supply air to the trailer system, then pull out the air supply knob to lock the trailer brakes -
ANS-You're hooking up a tractor and semi-trailer, and you've connected both air lines. Before
backing under the trailer, you should:
Directly in front of the trailer - ANS-When backing under a trailer, you should line up:
Hook up the emergency and service air lines. - ANS-You're hooking up a tractor to a semi-trailer
and have backed up but are not under it. What should you do before backing under the trailer?
At normal pressure - ANS-After pushing in the trailer supply valve, you should not move the
tractor
until air system is?
Reduce speed before entering turns. - ANS-There are two things you can do to prevent a
rollover. They are: Keep the cargo as close to the ground as possible, and:
3 psi - ANS-With the engine off and the brakes released, a combination vehicle air brake system
shouldn't leak more than how many psi in one minute?
The coupling is not correct and should be corrected before driving the coupled unit. - ANS-The
fifth wheel locking lever isn't locked after the jaws close around the kingpin. This means that:
If the trailer has no spring brakes, you could drive away, but you wouldn't have trailer brakes. -
ANS-You cross the air lines when hooking up to an old trailer. What will happen?
Fully raised with the crank handle secured - ANS-How far should you crank up the front trailer
supports after coupling a semi-trailer?
Usually do not have spring brakes - ANS-Air brake equipped trailers made before 1975
Never - ANS-The hand valve should be used to park a combination vehicle:
Red - ANS-Air lines on a combination vehicle are often colored to keep them from getting mixed
up. The emergency line is ____
By pushing in the trailer air supply valve. - ANS-How do you supply air to the air tank on the
trailer?
It should never be done. - ANS-In normal driving, some drivers use the hand valve before
applying the brake pedal to prevent trailer skids. Which of these statements is true?
Supply air to the trailer system, then pull out the air supply knob to lock the trailer brakes -
ANS-You're hooking up a tractor and semi-trailer, and you've connected both air lines. Before
backing under the trailer, you should:
Directly in front of the trailer - ANS-When backing under a trailer, you should line up:
