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CDL Practice Test: Air Brakes

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CDL Practice Test: Air Brakes

Air Brakes Questions

Click On The Picture To Begin

Good Luck!

If the air governor stops working properly, which of the following could occur?
  • All of these answers are correct
  • You may get increased condensation in your air tanks
  • The air system may not keep enough air pressure for safe driving
  • You could encounter steering difficulties
This is a question from page 45 - click here to look up the answer

Quote From Page 66 Of The Illinois CDL Manual:

Check air compressor governor cut-in and cut-out pressures:

Pumping by the air compressor should start at about 100 psi and stop at about 125 psi (check manufacturer?s specifications). Run the engine at a fast idle. The air governor should cut out the air compressor at about the manufacturer?s specified pressure. The air pressure shown by your gauge(s) will stop rising. With the engine idling, step on and off the brake to reduce the air tank pressure. The compressor should cut in at about the manufacturer?s specified cut-in pressure. The pressure should begin to rise.

If the air governor does not work as described above, it may need to be repaired. A governor that does not work right may not keep enough air pressure for safe driving.

TruckingTruth's Advice:

It is important to memorize the "cut in" and "cut out" levels for the air governor as well as the terminology.

Cut in: When the governor tells the air compressor to start pumping air into the air tanks. This should occur when air pressure falls to about 100 psi.

Cut out: When the governor tells the air compressor to stop pumping air into the air tanks. This should occur when the air pressure has risen to about 125 psi.

Next
While inspecting brake linings, all of the following statements are true except:
  • Linings must not be loose
  • Be sure linings have oil and grease on them to help prevent overheating
  • Be sure linings are not soaked with oil or grease
  • Linings must not be dangerously thin
This is a question from page 44 - click here to look up the answer

Quote From Page 66 Of The Illinois CDL Manual:

Check brake drums or discs, linings and hoses: Brake drums or discs must not have cracks longer than one-half the width of the friction area. Linings (friction material) must not be loose or soaked with oil or grease. They must not be dangerously thin. Mechanical parts must be in place, not broken or missing. Check the air hoses connected to the brake chambers to make sure they are not cut or worn due to rubbing.

TruckingTruth's Advice:

Brake linings can become covered with oil, grease, or other foreign matter kicked up from the roadway surface. Since oil and grease will greatly reduce the stopping power, be sure your brake linings are free from this type of debris.

Prev
Next
At what pressure will the air compressor governor tell the air compressor to "cut out"?
  • Around 125 psi
  • Around 75 psi
  • Around 150 psi
  • Around 100 psi
This is a question from page 41 - click here to look up the answer

Quote From Page 62 Of The Illinois CDL Manual:

When air tank pressure rises to the "cut-out" level (around 125 pounds per square inch, or "psi"), the governor stops the compressor from pumping air.

TruckingTruth's Advice:

Be sure to understand that the air compressor governor has one main purpose and that is to tell the air compressor when to pump air and when to stop pumping air. The air compressor governor will tell the air compressor to start supplying air (cut in) and when to stop supplying air (cut out).

  • Cut in air pressure is usually when air pressure falls to about 100 psi.
  • Cut out air pressure is usually when air pressure raises to about 125 psi
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Next
While inspecting the air compressor, you should:
  • Unbolt the air compressor from the engine as visually inspecting it while attached is nearly impossible
  • Visually check oil level inside the air compressor using a dip-stick
  • Check the condition and tightness of the belt (if belt driven)
  • Take the front cover off so you can look inside the vacuum seal
This is a question from page 44 - click here to look up the answer

Quote From Page 66 Of The Illinois CDL Manual:

Check air compressor drive belt if compressor is belt driven. If the air compressor is belt driven, check the condition and tightness of the belt. The belt should be in good condition.

TruckingTruth's Advice:

Some air compressors are gear driven, in which case, no belt will be present. Otherwise, be sure to check the belt to be sure it isn't frayed, cracked, off its tracks, or otherwise broken.

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Next
All of the following will increase your stopping distance, except:
  • Effective Braking Distance
  • Brake Lag Distance
  • Applied Friction Distance
  • Reaction Distance
This is a question from page 46 - click here to look up the answer

Quote From Page 68 Of The Illinois CDL Manual:

With air brakes, there is an added delay - the time required for the brakes to work after the brake pedal is pushed. With hydraulic brakes (used on cars and light/medium trucks), the brakes work instantly. However, with air brakes, it takes a little time (one-half second or more) for the air to flow through the lines to the brakes. Thus, the total stopping distance for vehicles with air brake systems is made up of four different factors:

Perception Distance
+ Reaction Distance
+ Brake Lag Distance
+ Effective Braking Distance
---------------------------
= Total Stopping Distance

TruckingTruth's Advice:

Be certain you have the stopping distance formula memorized as it will almost definitely show up on your written exam.

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Next
Which of these statements accurately defines the maximum amount of air loss allowed with the service brake released?
  • The loss rate should be less than 3 psi in 2 minutes for single vehicles and less than 4 psi in 2 minutes for combination vehicles
  • The loss rate should be less than 1 psi in 1 minute for single vehicles and less than 2 psi in 1 minute for combination vehicles
  • The loss rate should be less than 3 psi in 1 minute for single vehicles and less than 4 psi in 1 minute for combination vehicles
  • None of these answers are correct
This is a question from page 45 - click here to look up the answer

Quote From Page 66 Of The Illinois CDL Manual:

Test air leakage rate: With a fully-charged air system (typically 125 psi), turn off the engine, release the service brake, and time the air pressure drop. The loss rate should be less than 2 psi in 1 minute for single vehicles and less than 3 psi in 1 minute for combination vehicles. Then apply 90 psi or more with the brake pedal. After the initial pressure drop, if the air pressure falls more than 3 psi in 1 minute for single vehicles and more than 4 psi for combination vehicles, the air loss rate is too much. Check for air leaks, and repair before driving the vehicle. Otherwise, you could lose your brakes while driving.

TruckingTruth's Advice:

You really need to memorize the allowable air leakage rates. This will very likely come up on your written exam and will come up again during the pre-trip exam. Here's what you should memorize (create flash cards if you have to).

With the service brakes released (not depressing the brake pedal):

  • Air loss rate should be less than 2 psi in 1 minute for a single vehicle.
  • Air loss rate should be less than 3 psi in 1 minute for combination vehicles (vehicles with a trailer).

With the service brakes depressed (pressing the brake pedal):

  • Air loss rate should be less than 3 psi in 1 minute for a single vehicle.
  • Air loss rate should be less than 4 psi in 1 minute for combination vehicles (vehicles with a trailer).

Be sure to have that memorized. Very important!!

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Next
At about what psi should the air compressor stop pumping air into the air tanks?
  • 100 psi
  • 110 psi
  • 115 psi
  • 125 psi
This is a question from page 45 - click here to look up the answer

Quote From Page 66 Of The Illinois CDL Manual:

Check air compressor governor cut-in and cut-out pressures: Pumping by the air compressor should start at about 100 psi and stop at about 125 psi. (Check manufacturer's specifications.) Run the engine at a fast idle. The air governor should cut out the air compressor at about the manufacturer's specified pressure. The air pressure shown by your gauge(s) will stop rising. With the engine idling, step on and off the brake to reduce the air tank pressure. The compressor should cut in at about the manufacturer's specified cut-in pressure. The pressure should begin to rise.

Prev
Next
What is the proper braking technique on long or steep downgrades?
  • Apply the brakes enough to keep a constant speed during the entire downgrade
  • Begin the downgrade at a slow enough speed that brakes will not be necessary during the entire grade
  • Fluctuate between "hard braking" and "soft braking" but never fully release the brakes during a downgrade
  • Apply the brakes just hard enough to feel a definite slowdown, when your speed has been reduced to approximately 5mph below your "safe" speed, release the brakes and repeat as necessary
This is a question from page 47 - click here to look up the answer

Quote From Page 68 Of The Illinois CDL Manual:

Proper Braking Technique - Remember, the use of brakes on a long and/or steep downgrade is only a supplement to the braking effect of the engine. Once the vehicle is in the proper low gear, the following is the proper braking technique:

  • 1. Apply the brakes just hard enough to feel a definite slowdown.
  • 2. When your speed has been reduced to approximately 5 mph below your "safe" speed, release the brakes. (This brake application should last about 3 seconds.)
  • 3. When your speed has increased to your "safe" speed, repeat steps 1 and 2.
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