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CDL - COMBINATION VEHICLE PRACTICE TEST
QUESTIONS & ANSWERS 100% CORRECT
- A tractor with a(n) trailer requires the shortest amount of stop- ping distance.
1. empty
2. fully loaded
3. lightly loaded
ANS fully loaded
2. The air leakage rate for a combination vehicle ( engine off, brakes on)
should not be more than psi per minute.
- 4
- 6
- 2 ANS 4
3. If you do not do the final air brake check for air leaks and fix them before
driving,
- you could lose your brakes while driving
- your fuel usage will increase
- tire pressure will drop ANS you could lose your brakes while driving
- Which part of the kingpin should the locking jaws close around? ANS The shank
- Glad hands are used to connect the ....
1. kingpin from the trailer to the locking jaws of the fifth wheel
2. electrical lines from the tractor to the trailer
3. service and emergency air lines from the truck or tractor to the trailer
ANS ser- vice and emergency air lines from the truck or tractor to the trailer
- Trucks roll over more easily when fully loaded and are
1. ten times more likely to roll over in a crash than empty rigs
2. five times more likely to roll over in a crash than empty rigs
3. two times more likely to roll over in a crash than empty rigs
ANS ten times more likely to roll over in a crash than empty rigs
- In general, the higher your trucks center of gravity, the ...
1. easier it is to turn over
2. more stable it is when turning
3. easier it is to turn around corners
ANS easier it is to turn over
- 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 ...
1. the tractor to lose all air pressure
2. the tractor protection valve to close
3. the trailer supply valve to stay open
ANS the tractor protection valve to close
ANS applying and releasing the trailer brakes and listening for brake sounds
- If the brakes did not release when you pushed the trailer air supply valve, you should ...
1. cross the air lines,
2. check the air line connections
3. check the electrical cables
ANS check the air line connections
- You have a major leak in the service line, and you apply the brakes. Service air pressure will escape and cause the
1. trailer tank pressure to be lost
2. trailer emergency brakes to come on
3. tractor spring brakes to lock on
ANS trailer emergency brakes to come on
- You are uncoupling a trailer. After you shut off the trailer air supply and lock the trailer brakes, you should
1. immediately apply your tractor parking brakes
2. begin to lower the trailer landing gear
3. back up gently and ease pressure on the fifth wheel locking jaws
ANS back up gently to ease pressure on the fifth wheel locking jaws
- When should you use the hand valve to park a combination vehicle?
1. To park at loading docks
2. To park on a grade
3. never
ANS Never
- The front trailer supports are up, and the trailer is resting on the tractor. Make sure that
1. there is enough clearance between the upper and lower fifth wheel
2. there is enough clearance between the tractor frame and the landing gear
3. the safety latch is in the unlocked position
ANS there is enough clearance between the tractor frame and the landing gear
- The trailer hand valve works the trailer brakes. Which of these statements is true?
1. the foot brake sends air to all the brakes on the vehicle ( including the
trailer(s))
2. The trailer hand valve should be used only to test the trailer brakes
3. all the above
ANS all the above
- Where should the tractor be when you inspect the landing gear after uncoupling the trailer?
1. With the fifth wheel directly beneath the kingpin
1. A tractor pulling three trailers
2. A single tractor trailer
3. A tractor pulling two trailers
ANS A tractor pulling 3 trailers
- Air and electrical lines from the tractor to the trailer should be...
1. pulled tight with very little slack
2. secured but with enough slack for turns
3. resting on the frame of the tractor.
ANS secured but with enough slack for turns
- Compared with a straight truck or bus, there are things to inspect in combination vehicles.
1. fewer
2. more
3. the same number of
ANS more
- What is the emergency air line for?
1. To engage the trailer brakes in case of air pressure loss
2. To have extra air pressure in case you need it
3. To engage the front brakes of the tractor in case of an emergency
ANS To engage the trailer brakes in case of air pressure loss
- The tractor protection valve will close and the trailer brakes will come on when there is a major leak in the brake line.
1. parking
2. service
3. emergency
ANS emergency
- A trailer is most likely to jackknife when it is ...
1. loaded to full capacity
2. overloaded
3. empty
ANS empty
- When you are uncoupling a loaded trailer, lower the landing gear until it ...
1. reaches the ground
2. makes firm contact with the ground
3. makes contact with the ground, and leave the trailer off the fifth wheel
ANS -
makes firm contact with the ground
- How much space should there be between the upper and lower fifth wheel after coupling?
1. Just enough to see light through it
2. About 1/4 inch
3. None
ANS none
ANS if the air supply leaks away, there will be no brakes
- You are uncoupling a trailer. After you shut off the trailer air supply and lock the trailer brakes, you should
1. begin to lower the trailer landing gear
2. immediately apply your tractor parking brakes
3. back up gently to ease pressure on the fifth wheel locking jaw
ANS back up gently to ease pressure on the fifth wheel locking jaw
- While you are driving, your emergency air line breaks or gets pulled apart. The loss of pressure will cause the
1. air compressor to unload instead of pumping air
2. trailer emergency brakes to come on
3. trailer supply valve to open
ANS trailer emergency brakes to come on
- You are coupling a tractor to a semi-trailer. You have backed up but are not yet under it. Before backing under the semi trailer, you should hook up
1. the electrical service cable
2. nothing. Back up and lock the fifth wheel
3. The emergency and service air lines
ANS the emergency and service air lines
- When backing a tractor under a trailer, you should expect that
1. the trailer will be lifter slightly when the tractor backs under it
2. the trailer landing gear is fully extended
3. the end of the kingpin is even with the top of the fifth wheel
ANS the trailer will be lifting slightly when the tractor backs under it
- When you drive a set of doubles, which shut0off valve must be closed in the last trailer?
1. front
2. back
3. middle
ANS back
- What is a tractor jackknife?
1. When you lock up the drive tires on the trailer and the trailer spins out
sideways as the tractor continues to push forward
2. When you lock up the drive tires on the tractor and the tractor spins out
sideways as the trailer continues to push forward
3. Neither of the above
ANS When you lock up the drive tires on the tractor and the tractor spins out sideways as the trailer continues to push forward
