NC CDL COMBINATION VEHICLES
QUESTIONS AND ANSWERS
uYou are coupling a semi-trailer to your tractor but have not yet backed under, the trailer is at the right
height when: - It will be raised slightly when the tractor is backed under it.
You should not back a tractor under a trailer until the whole air system is: - At normal pressure.
Which part of the kingpin should the locking jaws close around? - The shank.
When you get ready to back under the semi-trailer you should line up: - Directly in front of the trailer.
How should you test the tractor semi-trailer connection for security? - Pull gently forward in low gear
against the locked trailer brakes, then look at it carefully.
When should you use the hand valve to park a combination vehicle? - Never.
You supply air to the trailer tanks by: - Pushing in the trailer air supply valve.
Why should you be sure that the fifth wheel plate is greased as required? - To prevent steering problems.
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: - Applying and releasing the trailer brakes and listening for brake sounds.
There are two things that a driver can do to prevent a rollover. They are: (1) Keep the cargo as close to
the ground as possible; and (2): - Go slowly around turns.
Before you back under a trailer, make sure the: - Trailer brakes are locked.
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? - Nothing is likely to happen until you try to apply the
brakes.
The air leakage rate for a combination vehicle (engine off, brakes on) should not be more than ___ PSI
per minute. - 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? - If the trailer has not spring brakes, you can drive away,
but you will not have trailer brakes.
Why should you lock the tractor glad hands (or dummy couplers) to each other when you are not towing
a trailer? - It will keep dirt and water out of the lines.
For coupling to be completed, the safety catch for the fifth wheel locking lever must be: - Over the
locking lever.
, The front trailer supports are up and trailer is resting on the tractor. Make sure: - There is enough
clearance between the tractor frame and the landing gear.
You have a major leak in the service line and you put on the brakes. Service air pressure will escape and
cause the: - Trailer emergency brakes to come on.
When backing under a tractor under a trailer you should expect: - Trailer will be lifted slightly when the
tractor backs under it.
The driver crosses the air lines when hooking up to an old trailer. What will happen? - If the trailer has no
spring brakes, you can drive away, but you will not have trailer brakes.
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 the semi-trailer? - The emergency and service air lines.
Air lines on a combination vehicle are often colored to keep them from getting mixed up. The emergency
line is ____; the service line is ____. - Red, blue
Which of these statements is true? - "Bobtail" tractors can take longer to stop than a combination
vehicle loaded to the maximum gross weight.
After connecting the air lines, but before backing under the trailer, you should: - Supply air to the trailer
system, then pull out the air supply knob.
The hand valve should be used: - To test the trailer brakes.
The air leakage rate for a combination vehicle (engine off, brakes off) should be no more than ___ PSI per
minute. - 3
The fifth wheel locking lever is not locked after the jaws close around the kingpin. This means that: - The
coupling is not right and should be fixed before driving the vehicle.
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: - The tractor protection valve to close.
Semi-trailers made before 1975 that are equipped with air brakes: - Often do not have spring brakes.
Almost half of all truck driver deaths are the result of: - Rollovers.
What statement best explains "crack the whip effect"? - When you make a quick lane change or sudden
movement with your steering wheel, the rear trailer tends to swing out. The force of the rear trailer
becomes amplified, causing it to roll over (rearward amplification).
Which type of truck-trailer combination has the best chance of the "crack the whip" rollover? - A tractor
pulling 3 trailers.
Which trailers are most likely to get stuck on railroad tracks? - Lowboy trailers. A low slung unit. Possum-
belly livestock trailers. A low slung unit. Single axle tractors pulling a short trailer. A low slung unit.
Where should the tractor be when you inspect landing gear after uncoupling the trailer? - With the
tractor frame under the trailer.
QUESTIONS AND ANSWERS
uYou are coupling a semi-trailer to your tractor but have not yet backed under, the trailer is at the right
height when: - It will be raised slightly when the tractor is backed under it.
You should not back a tractor under a trailer until the whole air system is: - At normal pressure.
Which part of the kingpin should the locking jaws close around? - The shank.
When you get ready to back under the semi-trailer you should line up: - Directly in front of the trailer.
How should you test the tractor semi-trailer connection for security? - Pull gently forward in low gear
against the locked trailer brakes, then look at it carefully.
When should you use the hand valve to park a combination vehicle? - Never.
You supply air to the trailer tanks by: - Pushing in the trailer air supply valve.
Why should you be sure that the fifth wheel plate is greased as required? - To prevent steering problems.
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: - Applying and releasing the trailer brakes and listening for brake sounds.
There are two things that a driver can do to prevent a rollover. They are: (1) Keep the cargo as close to
the ground as possible; and (2): - Go slowly around turns.
Before you back under a trailer, make sure the: - Trailer brakes are locked.
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? - Nothing is likely to happen until you try to apply the
brakes.
The air leakage rate for a combination vehicle (engine off, brakes on) should not be more than ___ PSI
per minute. - 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? - If the trailer has not spring brakes, you can drive away,
but you will not have trailer brakes.
Why should you lock the tractor glad hands (or dummy couplers) to each other when you are not towing
a trailer? - It will keep dirt and water out of the lines.
For coupling to be completed, the safety catch for the fifth wheel locking lever must be: - Over the
locking lever.
, The front trailer supports are up and trailer is resting on the tractor. Make sure: - There is enough
clearance between the tractor frame and the landing gear.
You have a major leak in the service line and you put on the brakes. Service air pressure will escape and
cause the: - Trailer emergency brakes to come on.
When backing under a tractor under a trailer you should expect: - Trailer will be lifted slightly when the
tractor backs under it.
The driver crosses the air lines when hooking up to an old trailer. What will happen? - If the trailer has no
spring brakes, you can drive away, but you will not have trailer brakes.
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 the semi-trailer? - The emergency and service air lines.
Air lines on a combination vehicle are often colored to keep them from getting mixed up. The emergency
line is ____; the service line is ____. - Red, blue
Which of these statements is true? - "Bobtail" tractors can take longer to stop than a combination
vehicle loaded to the maximum gross weight.
After connecting the air lines, but before backing under the trailer, you should: - Supply air to the trailer
system, then pull out the air supply knob.
The hand valve should be used: - To test the trailer brakes.
The air leakage rate for a combination vehicle (engine off, brakes off) should be no more than ___ PSI per
minute. - 3
The fifth wheel locking lever is not locked after the jaws close around the kingpin. This means that: - The
coupling is not right and should be fixed before driving the vehicle.
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: - The tractor protection valve to close.
Semi-trailers made before 1975 that are equipped with air brakes: - Often do not have spring brakes.
Almost half of all truck driver deaths are the result of: - Rollovers.
What statement best explains "crack the whip effect"? - When you make a quick lane change or sudden
movement with your steering wheel, the rear trailer tends to swing out. The force of the rear trailer
becomes amplified, causing it to roll over (rearward amplification).
Which type of truck-trailer combination has the best chance of the "crack the whip" rollover? - A tractor
pulling 3 trailers.
Which trailers are most likely to get stuck on railroad tracks? - Lowboy trailers. A low slung unit. Possum-
belly livestock trailers. A low slung unit. Single axle tractors pulling a short trailer. A low slung unit.
Where should the tractor be when you inspect landing gear after uncoupling the trailer? - With the
tractor frame under the trailer.
