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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 Tennessee CDL knowledge test. The TN 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 Tennessee CDL Manual. Take this TN CDL practice test now to prepare for the actual air brakes test!
1. Which of the following is NOT a reason for hydraulic brake failure?
Loss of hydraulic pressure
Stab braking
Brake fade on long hills
All of the above.
2. To operate a vehicle equipped with air brakes, you must pass the air brakes knowledge test. Why?
If you don't pass the air brakes test, you can't get a CDL.
If you don't pass the air brakes test, you will be restricted to driving vehicles without air brakes.
All trucks have air brakes.
If you don't, you will only receive a CDL permit.
3. If your vehicle is hydroplaning, you should:
release the accelerator and push in the clutch.
use the brakes to slow down.
accelerate to get through the water as quickly as possible.
None of the above.
4. The ________ brake system applies and releases the brakes when the driver uses the brake pedal during normal driving.
5. The Johnson bar is a valve that:
works the trailer brakes.
is installed in the first tank the air compressor pumps air to.
keeps air from going out if the air compressor develops a leak.
reduces the braking pressure to a safe level.
6. The most common foundation brakes found on vehicles with air brakes are the:
wedge brakes.
parking brakes.
disc brakes.
S-cam brakes.
7. When the spring brakes are on, you should push the brake pedal down:
Only when driving downhill.
Only when driving uphill.
Only when approaching railroad-highway crossings.
8. If your vehicle does not have automatic air tank drains, how often should you drain air tanks to remove moisture and oil?
Once a week.
At the end of each working day.
Every 4 hours.
At least once a month.
9. To test the low pressure warning signal, you should:
pump the brakes while your vehicle is running.
shut the engine off when you have enough air pressure, turn the electrical power on and step on and off the brake pedal until the low air pressure warning signal comes on.
manually let the air out of your brakes and see if the signal comes on.
check the air hoses connected to the brake chambers to make sure they aren't cut.
10. Supply pressure gauges tell you:
when the air pressure in the tanks falls below 60 psi.
how much air pressure you are applying to the brakes.
how much pressure is in the air tanks.
when the pressure in the system drops below 60 psi.
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TN CDL Air Brakes Test

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