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CDL Practice Test: Combination Vehicles

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CDL Practice Test: Combination Vehicles

Combination Vehicles Questions

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Good Luck!

Which statement about inspecting a combination vehicle is false?
  • Make sure the fifth wheel locking jaws are around the head of the kingpin and not the shank of the kingpin
  • Check the the air lines and electrical line to be certain they are properly secured and connected
  • Be sure the landing gear is fully raised, no missing parts, not bent or otherwise damaged
  • If you have a sliding fifth wheel, you must make sure the fifth wheel is securely locked in place
This is a question from page 54 - click here to look up the answer

Quote From Page 78 Of The Illinois CDL Manual:

Inspecting a Combination Vehicle

  • Locking jaws around the shank, not the head of kingpin.
  • Landing gear is fully raised, no missing parts, not bent or otherwise damaged.
  • Air lines properly connected to glad hands, no air leaks, properly secured with enough slack for turns.
  • All sliding fifth wheel locking pins present and locked in place
Next
Why shouldn't you use the trailer hand valve while driving?
  • There is an increased danger of making the trailer skid
  • It can throw your brakes out of adjustment
  • It only applies braking force to the tractor brakes
  • You may wear out the tractor brakes more quickly
This is a question from page 49 - click here to look up the answer

Quote From Page 73 Of The Illinois CDL Manual:

The trailer hand valve should be used only to test the trailer brakes. Do not use it in driving because of the danger of making the trailer skid. The foot brake sends air to all the brakes on the vehicle (including the trailer(s'). There is much less danger of causing a skid or jackknife when using just the foot brake.

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Next
The air pressure range when the tractor protection valve will pop out occurs at:
  • Between 20 and 45 psi
  • Between 50 and 75 psi
  • Between 100 and 120 psi
  • Between 5 and 15 psi
This is a question from page 54 - click here to look up the answer

Quote From Page 79 Of The Illinois CDL Manual:

The trailer air supply control (also called the tractor protection valve control) should pop out or go from "normal" to "emergency" position) when the air pressure falls into the pressure range specified by the manufacturer (usually within the range of 20 to 45 psi).

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What are Glad Hands?
  • A name for the yellow and red air valves in the cab of a truck
  • Caps which cover the valve stems on tires
  • Coupling devices used to connect the service and emergency air lines from the truck or tractor to the trailer
  • Used to secure the trailer kingpin to the tractor 5th wheel
This is a question from page 50 - click here to look up the answer

Quote From Page 73 Of The Illinois CDL Manual:

"Glad hands" are coupling devices used to connect the service and emergency air lines from the truck or tractor to the trailer.

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When pulling a single trailer with a Shut-Off Valve, the valves must be in the:
  • Closed position
  • Open position
  • Stopped position
  • Off position
This is a question from page 50 - click here to look up the answer

Quote From Page 74 Of The Illinois CDL Manual:

You must check that all shut-off valves are in the open position except the ones at the back of the last trailer, which must be closed.

TruckingTruth's Advice:

When only pulling one trailer, be sure the shut-off valves are all in the fully closed position.

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What happens when there is a major leak in the emergency air line?
  • It will disable the emergency brakes
  • Nothing will happen, but an in-cab warning indicator will let you know about the problem
  • It will cause the tractor protection valve to open and the trailer emergency brakes to come on
  • It will cause the tractor protection valve to close and the trailer emergency brakes to come on
This is a question from page 50 - click here to look up the answer

Quote From Page 74 Of The Illinois CDL Manual:

A major leak in the emergency line will cause the tractor protection valve to close and the trailer emergency brakes to come on.

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What might happen if the trailer is too high when you try to couple?
  • Modern trucks are installed with a "trailer height icon" which will illuminate on your dashboard
  • The fifth wheel plate will automatically adjust to the trailer height
  • It may not couple correctly
  • The trailer will be forced downward into the fifth wheel plate, causing damage to the ground or landing gear
This is a question from page 51 - click here to look up the answer

Quote From Page 75 Of The Illinois CDL Manual:

Check Trailer Height

  • The trailer should be low enough that it is raised slightly by the tractor when the tractor is backed under it. Raise or lower the trailer as needed. (If the trailer is too low, the tractor may strike and damage the nose of the trailer; if the trailer is too high, it may not couple correctly.)
  • Check that the kingpin and fifth wheel are aligned.

TruckingTruth's Advice:

In addition to incorrect coupling, if a trailer is too high off the ground and you try to back into it, you may cause damage as the rear of your truck cab could strike the front of the trailer. Further, the trailer king pin may become stuck in front of the fifth wheel plate which can be a costly and time wasting error. Before backing under any trailer, it's very important to visually check the trailer height in relation to your tractors fifth wheel.

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The Tractor Protection Valve will close automatically in what air pressure range
  • 0 to 25 psi
  • 50 to 75 psi
  • 20 to 45 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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