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The air brakes endorsement applies to applicants who wish to drive a vehicle with air brakes in Class A, B, or C CDL. To drive a vehicle with air brakes, you must pass the air brake component of the North Carolina CDL knowledge test. The NC CDL air brakes test consists of 25 questions, and you'll need at least 20 correct answers to pass (80%). The test covers the information found in the air brakes section of the North Carolina CDL Manual. Take this NC CDL practice test now to prepare for the actual air brakes test!
1. Before leaving your vehicle unattended, you should:
Chock the wheels.
Apply the parking brake.
Remove the keys.
All of the above.
2. Why must air tanks be drained?
To keep from fouling the air compressor oil.
Water and oil reduce the air pressure.
The low boiling point of water reduces braking power.
Water can freeze in cold weather and cause brake failure.
3. Which of the following is not part of the air brake system?
Air compressor
Alcohol evaporator
Air storage tanks
Air filter
4. Some air brake systems have an alcohol evaporator to:
prevent ice from forming in the brake system.
reduce the stopping power of the vehicle.
reduce the danger of slipping.
force the brake shoes away from one another.
5. Which of the following is NOT part of the drum brake?
Brake drum
Return spring
Safety valve
6. If your vehicle is equipped with air brakes, loss of air pressure in the emergency line causes:
the trailer emergency brakes to come on.
the speed of your vehicle to increase.
the trailer spring brakes to come on.
All of the above.
7. The stop light switch:
turns on the brake lights when you put on the air brakes.
should be used to fend off tailgaters.
warns you when the air supply pressure drops below 55 psi.
tells you when you need to use your parking brake instead of the service brake.
8. When going down a steep downgrade, you should:
use the parking brake.
avoid braking and rely on engine braking.
use a low gear, and a proper braking technique.
use escape ramps whenever possible.
9. To check slack adjusters on S-cam brakes, you should:
use gloves and pull hard on each slack adjuster you can reach.
press the brake pedal and listen for any strange noises.
check that the spring brakes come on automatically.
All of the above.
10. An ABS system:
keep your wheels from locking when you brake hard.
gives you more control over the vehicle during braking.
helps you avoid skids caused by over braking.
All of the above.
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NC CDL Air Brakes Test

Number of questions: 25
Correct answers to pass:20
Passing score:80%
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