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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 Missouri CDL knowledge test. The MO 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 Missouri CDL Manual. Take this MO CDL practice test now to prepare for the actual air brakes test!
1. You must take the CDL skills tests in the type of vehicle for which you wish to be licensed. If your test vehicle does not have air brakes:
you'll need to take another knowledge test about air brakes.
you'll have to immediately retake your test using another vehicle.
you will be restricted to driving vehicles without air brakes.
2. Typically an air system is fully-charged at:
75 psi
125 psi
25 psi
3. If your vehicle does not have automatic air tank drains, how often should you drain air tanks to remove moisture and oil?
Every 4 hours.
Once a week.
At the end of each working day.
4. The ________ brake system applies and releases the brakes when the driver uses the brake pedal during normal driving.
5. You are driving on a steep downgrade. If your safe speed is 35 mph, you should apply the brakes when your speed reaches:
25 mph
30 mph
35 mph
6. If you must make an emergency stop, you should:
apply the brakes as hard as you can to lock them.
use the hand brake before the brake pedal.
brake in a way that will keep your vehicle in a straight line.
7. Tar in the road pavement rising to the road surface in very hot weather:
causes the road to become very slippery.
does not affect the road surface or driving conditions.
is very sticky and will slow down your vehicle.
8. Which of the following is a reason why air tanks must be drained?
The governor may stop the compressor from pumping air.
Your brakes may fail due to the water freezing.
Your battery fluid may drain out.
9. How do you check that spring brakes come on automatically?
On a tractor-trailer combination vehicle, continue to step on and off the brake pedal until the tractor protection valve and the parking brake valve close.
Continue to step on and off the brake pedal until the air pressure falls to the manufacturer’s specification.
All of the above.
10. The alcohol evaporator:
ensures the coolant temperature gauge remains in the normal range.
helps to reduce the risk of ice in air brake valves and other parts in cold weather.
eliminates the need for daily air tank drainage.
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MO Air Brakes CDL 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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