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CDL Combination Vehicles Study Guide #1
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You should not back a tractor under a trailer until the whole air system is:
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Between 60 and 80 PSI
At normal pressure
Bled down to half the maximum pressure
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?
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Nothing is likely to happen until you try to apply the brakes
The trailer’s air tank will exhaust through the open line
The emergency tractor brakes will come on
In normal driving, some drivers use the hand valve before applying the brake pedal to prevent a jackknife. Which of these statements is true?
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The hand valve should not be used to slow the vehicle when driving
The brake pedal will work the trailer spring brakes instead of the air brakes
The hand valve will apply the tractor brakes instead of the trailer brakes
Why should you lock the tractor glad hands to each other or use "dummy couplers" when you are not towing a trailer?
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The connected brake circuit becomes a backup air tank
If you did not, you could never build system pressure
It will keep dirt and water out of the lines
When should you use the hand valve to park a combination vehicle?
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To park at loading docks
Never
To park on a grade
The air leakage rate for a combination vehicle (engine off, brakes on) should not be more than ___ PSI per minute.
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4
2
6
How should you test the tractor semi-trailer connection for security?
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Pull gently forward in low gear against the locked trailer brakes, then look at it carefully
Put the tractor in gear and pull ahead with a sharp jerk
Rock the trailer back and forth with the trailer brakes locked
Which of these statements is true?
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Light vehicles need more braking power to stop than heavy ones
Always delay braking a heavy vehicle until you have no other choice
“Bobtail” tractors can take longer to stop than a combination vehicle loaded to the maximum gross weight
Almost half of all truck driver deaths are the result of:
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Speed
Rollovers
Following too closely
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:
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The trailer supply valve to stay open
The tractor to lose all air pressure
The tractor protection valve to close
Why should you be sure that the fifth wheel plate is greased as required?
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To reduce heat and noise
To prevent steering problems
To ensure good electrical connections
You are coupling a semi-trailer to your tractor but have not yet backed under, the trailer is at the right height when:
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It will be raised slightly when the tractor is backed under it
The kingpin is about 1 ¼ inches above the fifth wheel
The end of the kingpin is even with the top of the fifth wheel
The driver crosses the air lines when hooking up to an old trailer. What will happen?
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If the trailer has no spring brakes, you can drive away, but you will not have trailer brakes
The brake pedal will work the trailer spring brakes instead of the air brakes
The hand valve will apply the tractor brakes instead of the trailer brakes
For coupling to be completed, the safety catch for the fifth wheel locking lever must be:
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Straight up
Over the locking lever
Through the locking lever
The air leakage rate for a combination vehicle (engine off, brakes off) should be no more than ___ PSI per minute.
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2
3
4
Which part of the kingpin should the locking jaws close around?
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The base
The shank
The head
Air lines on a combination vehicle are often colored to keep them from getting mixed up. The emergency line is ____; the service line is ____.
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Red, blue
Blue, red
Black, yellow
Before you back under a trailer, make sure the:
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Air supply knob is in
Air brakes are off
Trailer brakes are locked
You supply air to the trailer tanks by:
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Pushing in the trailer air supply valve
Pulling out the trailer air supply valve
Connecting the service line glad hand
You have a major leak in the service line and you put on the brakes. Service air pressure will escape and cause the:
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Trailer tank pressure to be lost
Trailer emergency brakes to come on
Tractor spring brakes to lock on
Semi-trailers made before 1975 that are equipped with air brakes:
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Often do not have spring brakes
Usually need to a glad hand converter
Are easier to brake because they are heavier
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?
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The emergency and service air lines
The electrical service cable
Nothing, back up and lock the fifth wheel
When backing a tractor under a trailer you should expect:
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Trailer will be lifted slightly when the tractor backs under it
End of the kingpin is even with the top of the fifth wheel
Trailer landing gear is fully extended
The fifth wheel locking lever is not locked after the jaws close around the kingpin. This means that:
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You can set the fifth wheel for weight balance
The coupling is not right and should be fixed before driving the vehicle
The parking lock is off and you may drive away
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):
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Make sure that the brakes are properly adjusted
Keep the fifth wheel’s free play as tight as possible
Go slowly around turns
When you get ready to back under the semi-trailer you should line up:
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About 12 degrees off the line of the trailer
The kingpin to engage the driver’s side locking jaw first
Directly in front of the trailer
The front trailer supports are up and trailer is resting on the tractor. Make sure:
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There is enough clearance between the upper and lower fifth wheel
The safety latch is in the unlocked position
There is enough clearance between the tractor frame and the landing gear
The hand valve should be used:
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To test the trailer brakes
Only when the trailer is fully loaded
Only with the foot brake
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:
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Applying and releasing the trailer brakes and listening for brake sounds
Turning on the parking brakes from the cab
Lifting the brake pedal
After connecting the air lines, but before backing under the trailer, you should:
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Make sure that the trailer brakes are off
Supply air to the trailer system, then pull out the air supply knob
Walk around the rig to make sure it is clear
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