Combination Vehicle #1
You should not back a tractor under a trailer until the whole air system is
At normal pressure
Between 60 and 80 psi
Bled down to half the maximum pressure
Disconnected
Before you back under a trailer, make sure the:
Trailer electrics are connected
At normal pressure
Trailer brakes are locked
Air brakes are off
You 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
The trailer drops in place with a bang
The kingpin is about 1 1/4inches above the fifth wheel
The end of the kingpin is even with the top of the fifth wheel
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 electrical service cable
The emergency and service air lines
Nothing: back up and lock the fifth wheel
The emergency and service air lines & The electrical service cable
When you get ready to back under the semi-trailer you should line up:
Directly in front of the trailer
About 12 degrees off the line of the trailer
The kingpin to engage the driver’s side locking jaw first
Anywhere that is convenient
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?
The air compressor will discharge to the supply tank.
Nothing is likely to happen until you try to apply the brakes
The emergency tractor brakes will come on.
The trailer’s air tank will exhaust through the open line.
Which part of the kingpin should the locking jaws close around?
The head
The base
The shank
Anywhere is fine
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 coupled unit.
The parking lock is off and you may drive away.
You can set the fifth wheel for weight balance.
You will have to drive slowly until it locks.
How should you test the tractor semi-trailer connection for security?
Put the tractor in gear and pull ahead with a sharp jerk
Pull gently forward in low gear against the locked trailer brakes. Then look at it carefully.
Get up to speed, then turn sharply
Rock the trailer back and forth with the trailer brakes locked
The air leakage rate for a combination vehicle (engine off, brakes on) should be less than ________ psi per minute.
4
3
2
1
When should you use the hand valve to park a combination vehicle?
To park at loading docks
Always
To park on a grade
Never
You have coupled with a semi-trailer. In what position should you put the front trailer supports before driving away?
Fully raised with the crank handle secured in its bracket
Three turns off the top with the crank handle secured in its bracket
Raised half way with the crank handle removed
Just far enough to not drag
You supply air to the trailer tanks by:
Connecting the service line glad hand
Pushing in the trailer air supply valve
Starting the engine
Pulling out the trailer air supply valve
In normal driving, some drivers use the hand valve before applying the brake pedal to prevent a jackknife. Which of these statements is true?
It will lock the tractor brakes.
It should not be done.
It results in less skidding than using the brake pedal alone.
It is the best way to brake and keep the truck in a straight line.
The air leakage rate for a combination vehicle (engine off, brakes off) should be less than __________ psi per minute.
4
3
2
1
Why should you be sure that the fifth wheel plate is greased as required?
To reduce heat and noise
To prevent sparks from flying
To ensure good electrical connections
To prevent steering problems
A driver crosses the air lines when hooking up to an old trailer. What will happen?
The hand valve will apply the tractor brakes instead of the trailer brakes.
Nothing, the brakes will work as normal.
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.
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:
Turning on the parking brakes from the cab
Testing the brakes at a slow speed
Lifting the brake pedal
Applying and releasing the trailer brakes and listening for brake sounds
Air lines on a combination vehicle are often colored to keep them from getting mixed up. The emergency line is __________: the service line is ________.
Blue; red
Black; yellow
Red; black
Red; blue
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)
Keep the fifth wheel’s free play as tight as possible
Make sure that the brakes are properly adjusted
Go slowly around turns
Observe the posted speed limit
Semi-trailers made before 1975 that are equipped with air brakes:
Are easier to brake because they are heavier
Are unsafe and should not be used
Often do not have spring brakes
Usually need a glad hand converter
Which of these statements are true?
If you start to jackknife, apply the trailer hand valve to straighten out the trailer.
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.
Why should you lock the tractor glad hands (or dummy couplers) to each other when you are not towing a trailer?
The connected brake circuit becomes a back up air tank.
It will keep dirt and water out of the lines.
Reserve air pressure will be maintained under all conditions.
If you did not, you could never build system pressure.
The hand valve should be used:
Only when parking
Only with the foot brake
To test the trailer brakes
Only when the trailer is fully loaded
The safety catch for the fifth wheel locking lever must be _____________ for a coupling to be complete.
Behind the locking lever
Over the locking lever
Through the locking lever
Under the locking lever
You are coupling a tractor and semi-trailer and have connected the air lines. Before backing under the trailer, you should:
Push in the trailer air supply knob
Apply the brakes twice to alert others
Make sure that the trailer brakes are off
Supply air to the trailer system, then pull out the air supply knob to lock the trailer brakes.
The front trailer supports are up and the trailer is resting on the tractor. Make sure:
There is enough clearance between the tops of the tractor tires and the nose of the trailer
There is enough clearance between the tractor frame and the landing gear
Both answers are correct
None of the answers are correct
Your emergency air line breaks or gets pulled apart while you are driving. The loss of pressure will cause:
Emergency trailer brakes to come on
Trailer supply valve to close
Trailer supply valve to open
Air compressor to unload instead of pumping air
You have a major leak in the service line and you put on the brakes. Service air pressure will escape and cause the:
Tractor spring brakes to lock on
Tractor emergency brakes to come on
Trailer emergency brakes to come on
Trailer tank pressure to be lost
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 stay open
The tractor protection valve to close
The tractor to lose all air pressure
The trailer supply valve to stay open
How much space should be between the upper and lower fifth wheel after coupling?
One to two inches
None
At least 1/2 inch
Just enough to see light through it
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