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CDL Practice Test: Combination Vehicles

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CDL Practice Test: Combination Vehicles

Combination Vehicles Questions

Click On The Picture To Begin

Good Luck!

Which device inside the cab of a truck controls the Tractor Protection Valve
  • The red "trailer air supply" control valve
  • The yellow "parking brake" control valve
  • The trailer hand valve
  • The brake pedal
This is a question from page 49 - click here to look up the answer

Quote From Page 73 Of The Illinois CDL Manual:

The tractor protection valve keeps air in the tractor or truck should the trailer break away or develop a bad leak. The tractor protection valve is controlled by the "trailer air supply" control valve in the cab. The control valve allows you to open and shut the tractor protection valve. The tractor protection valve will close automatically if air pressure is low (in the range of 20 to 45 psi). When the tractor protection valve closes, it stops any air from going out of the tractor. It also lets the air out of the trailer emergency line. This causes the trailer emergency brakes to come on.

Next
How are the trailer air tanks filled?
  • Using the emergency air line
  • Using a combination of the emergency air line and the service air line
  • Using the service air line
  • Using the trailer tank line
This is a question from page 50 - click here to look up the answer

Quote From Page 74 Of The Illinois CDL Manual:

Each trailer and converter dolly has one or more air tanks. They are filled by the emergency (supply) line from the tractor. They provide the air pressure used to operate trailer brakes.

TruckingTruth's Advice:

The service air line is only used to control the service brakes (when you press on the brake pedal or use the trailer hand-valve). All other trailer air functions use the emergency line.

Prev
Next
All of the following are good ways to inspect the tractor and trailer coupling, except:
  • Check to make sure there is about 3 to 6 inches of space between the fifth wheel plate and the trailer
  • Be sure the safety latch is in position over the locking lever
  • Raise the trailer landing gear slightly off the ground and pull the tractor gently forward with the trailer brakes set to be sure you are connected
  • Go under the trailer and look into the back of the fifth wheel to be sure the trailer king pin is properly secured in the fifth wheel locking jaws
This is a question from page 52 - click here to look up the answer

Quote From Page 75 Of The Illinois CDL Manual:

Check Connection For Security

  • Raise trailer landing gear slightly off ground.
  • Pull tractor gently forward while trailer brakes are still locked to check that the trailer is locked onto the tractor.

Secure Vehicle

  • Put transmission in neutral.
  • Put parking brakes on.
  • Shut off engine and take key with you so someone else will not move truck while you are under it

Inspect Coupling

  • Use a flashlight if necessary.
  • Make sure there is no space between upper and lower fifth wheel. If there is space, something is wrong (kingpin may be on top of closed fifth wheel jaws; trailer would come loose very easily).
  • Go under trailer and look into the back of the fifth wheel. Make sure the fifth wheel jaws have closed around the shank of the kingpin.
  • Check that locking lever is in the "lock" position.
  • Check that safety latch is in position over locking lever. (On some fifth wheels, the latch must be put in place by hand.)
  • If the coupling is not right, do not drive the coupled unit; get it repaired
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Next
The Tractor Protection Valve will close automatically in what air pressure range
  • 50 to 75 psi
  • 20 to 45 psi
  • 0 to 25 psi
  • 90 to 110 psi
This is a question from page 49 - click here to look up the answer

Quote From Page 73 Of The Illinois CDL Manual:

The tractor protection valve will close automatically if air pressure is low (in the range of 20 to 45 psi).

TruckingTruth's Advice:

It is definitely worth memorizing the psi range the tractor protection valve will automatically close. Not only will you need to know this for the written and pre-trip exams, but you'll definitely want to know this info for real-world driving situations and when testing the air brake system.

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Next
Which of the following can help reduce the chance of a truck rollover?
  • All of these can help reduce the chance of a truck rollover
  • Look far enough down the road to avoid being surprised and having to make a sudden lane change
  • Slow down to a safe speed before going into a turn
  • At night, drive slow enough to see obstacles with your headlights before it is \ too late to change lanes or stop gently
This is a question from page 48 - click here to look up the answer

Quote From Page 70 Of The Illinois CDL Manual:

Steer gently and smoothly when pulling trailers. If you make a sudden movement with your steering wheel, you could tip over. Follow far enough behind other vehicles (at least 1 second for each 10 feet of your vehicle length, plus another second if going over 40 mph). Look far enough down the road to avoid being surprised and having

Prev
Next
Trailers built before what year may not be equipped with trailer spring brakes?
  • 1990
  • 1970
  • 1985
  • 1975
This is a question from page 50 - click here to look up the answer

Quote From Page 74 Of The Illinois CDL Manual:

Newer trailers have spring brakes just like trucks and truck tractors. However, converter dollies and trailers built before 1975 are not required to have spring brakes. Those that do not have spring brakes have emergency brakes that work from the air stored in the trailer air tank. The emergency brakes come on whenever air pressure in the emergency line is lost. These trailers have no parking brake. The emergency brakes come on whenever the air supply knob is pulled out or the trailer is disconnected. But the brakes will hold only as long as there is air pressure in the trailer air tank. Eventually, the air will leak away, and then there will be no brakes. Therefore, it is very important for safety that you use wheel chocks when you park trailers without spring brakes.

TruckingTruth's Advice:

It is extremely unlikely you will drive a trailer built before 1975, but for the written exam, you still may need to know that trailers built before 1975 were not required to have spring brakes.

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Next
How should you position your tractor before backing under and connecting to a trailer?
  • Back the tractor to the trailer on the left side
  • Back the tractor directly in front of the trailer
  • Back the tractor to the trailer at a 45 degree angle on either the left or right side
  • Back the tractor to the trailer on the right side
This is a question from page 51 - click here to look up the answer

Quote From Page 75 Of The Illinois CDL Manual:

  • Put the tractor directly in front of the trailer. (Never back under the trailer at an angle because you might push the trailer sideways and break the landing gear.)
  • Check position, using outside mirrors, by looking down both sides of the trailer.

TruckingTruth's Advice:

It will take some practice, but always back under a trailer as straight as possible to avoid turning the trailer over.

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Next
Before disconnecting from a trailer, you should:
  • Set the tractor parking brakes but wait to set the trailer spring brakes until the landing gear has been lowered and the air lines have been disconnected
  • Set the trailer spring brakes but wait to set the tractor parking brakes until the landing gear has been lowered and the air lines have been disconnected
  • Apply the trailer spring brakes, then gently pull forward against the trailer to apply tension onto the fifth wheel locking lever
  • Apply the trailer spring brakes, then back up gently towards the trailer to ease tension off the fifth wheel locking lever
This is a question from page 53 - click here to look up the answer

Quote From Page 77 Of The Illinois CDL Manual:

Ease Pressure on Locking Jaws

  • Shut off trailer air supply to lock trailer brakes.
  • Ease pressure on fifth wheel locking jaws by backing up gently. (This will help you release the fifth wheel locking lever.)
  • Put on parking brakes while tractor is pushing against the kingpin. (This will hold rig with pressure off the locking jaws.
Prev
Finish
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