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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!

How are the trailer air tanks filled?
  • Using the emergency air line
  • Using the trailer tank line
  • Using a combination of the emergency air line and the service air line
  • Using the service air 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.

Next
What does the Service Air Line do?
  • Controls the emergency brakes
  • Carries air controlled by the foot brake or the trailer hand brake
  • Controls the parking brakes
  • Supplies air to the trailer air tanks
This is a question from page 49 - click here to look up the answer

Quote From Page 73 Of The Illinois CDL Manual:

The service line (also called the "control line" or "signal line") carries air controlled by the foot brake or the trailer hand brake. Depending on how hard you press the foot brake or hand valve, the pressure in the service line will similarly change. The service line is connected to relay valves. These valves allow the trailer brakes to be applied more quickly than would otherwise be possible.

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Next
Before coupling a tractor to a trailer, the Fifth Wheel should:
  • Be put in the manual lock position
  • Be free of oil and grease
  • Have the jaws closed
  • Be tilted down towards the rear of the tractor
This is a question from page 51 - click here to look up the answer

Quote From Page 75 Of The Illinois CDL Manual:

Inspect Fifth Wheel Check for damaged/missing parts.

  • Check to see that mounting to tractor is secure, no cracks in frame, etc.
  • Be sure that the fifth wheel plate is greased as required. Failure to keep the fifth wheel plate lubricated could cause steering problems because of friction between the tractor and trailer.
  • Check if fifth wheel is in proper position for coupling:
    • Wheel tilted down towards rear of tractor.
    • Jaws open.
    • Safety unlocking handle in the automatic lock position.
  • If you have a sliding fifth wheel, make sure it is locked.
  • Make sure the trailer kingpin is not bent or broken.
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Next
What is the best way to test the Trailer Service Brakes?
  • Check for normal air pressure, release the parking brakes, move the vehicle forward slowly, and apply trailer brakes with the hand control (trolley valve), if so equipped
  • With the engine off, step on and off the brake pedal several times to reduce the air pressure in the tanks and make sure the tractor protection valve pops out
  • Pull out the trailer air supply control and pull gently on the trailer with the tractor to make sure the brakes work
  • Release all brakes except the trailer service brakes using the trailer hand control valve (trolley valve) then walk back to the rear of the trailer and visually check to be sure the brakes are engaged
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 service brakes: Check for normal air pressure, release the parking brakes, move the vehicle forward slowly, and apply trailer brakes with the hand control (trolley valve), if so equipped. You should feel the brakes come on. This tells you the trailer brakes are connected and working. (The trailer brakes should be tested with the hand valve but controlled in normal operation with the foot pedal, which applies air to the service brakes at all wheels.)

TruckingTruth's Advice:

Many companies are no longer installing trailer hand control valves which is very unfortunate as this is really the only way to be certain the trailer service brakes are functioning properly. If your truck does not come equipped with a trailer hand control valve, test your brakes before you start driving on a major roadway. If you notice the truck struggling to stop, the problem most likely is with your trailer brakes and needs to be inspected.

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What is the Trailer Hand Valve used for?
  • Can be used in place of the parking brake
  • During long or steep declines, the trailer hand valve should be used to protect against tractor brake fade
  • Should be used to recover a trailer that has begun to jackknife
  • It is only used to test the trailer service brakes
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 (also called the "trolley valve" or "Johnson bar") works the trailer brakes. 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.

Never use the hand valve for parking because all the air might leak out, unlocking the brakes (in trailers that do not have spring brakes.) Always use the parking brakes when parking. If the trailer does not have spring brakes, use wheel chocks to keep the trailer from moving.

TruckingTruth's Advice:

Many trucks no longer come with a trailer hand valve, but if your truck has one, you should use it only for testing the trailer service brakes and nothing more.

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Next
What happens if you cross the Emergency Air Line and the Service Air Line?
  • Air will continue filling the air holding tanks until the tanks rupture from excessive pressure
  • Supply air will cause all brakes to release and the truck will roll freely without any braking ability
  • Supply air will be sent to the service line instead of going to charge the trailer air tanks which means the trailer spring brakes will not release
  • Newer vehicles automatically detect if the lines are crossed and will auto-correct itself
This is a question from page 50 - click here to look up the answer

Quote From Page 73 Of The Illinois CDL Manual:

If you do cross the air lines, supply air will be sent to the service line instead of going to charge the trailer air tanks. Air will not be available to release the trailer spring brakes (parking brakes). If the spring brakes do not release when you push the trailer air supply control, check the air line connections.

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Next
Which statement about inspecting a combination vehicle is false?
  • Be sure the landing gear is fully raised, no missing parts, not bent or otherwise damaged
  • Check the the air lines and electrical line to be certain they are properly secured and connected
  • If you have a sliding fifth wheel, you must make sure the fifth wheel is securely locked in place
  • Make sure the fifth wheel locking jaws are around the head of the kingpin and not the shank of the kingpin
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
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When dropping an empty trailer, you should lower the landing gear until:
  • It makes firm contact with the ground
  • You can't turn the landing gear handle any further
  • The landing gear is 1 to 3 inches above the ground
  • None of these answers are correct
This is a question from page 53 - click here to look up the answer

Quote From Page 77 Of The Illinois CDL Manual:

Lower the Landing Gear

  • If trailer is empty, lower the landing gear until it makes firm contact with the ground.
  • If trailer is loaded, after the landing gear makes firm contact with the ground, turn crank in low gear a few extra turns. This will lift some weight off the tractor. (Do not lift trailer off the fifth wheel.) This will make it easier to unlatch the fifth wheel and easier to couple next time.
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Finish
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[1,2,4,1,4,3,4,1]
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