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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 District of Columbia CDL knowledge test. The DC 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 District of Columbia CDL Manual. Take this DC CDL practice test now to prepare for the actual air brakes test!
1. What should you do to test your vehicle's low air pressure warning signal?
Release the parking brake valve and the tractor protection valve and reduce the air pressure by stepping on and off the brake pedal.
With the engine running, put the vehicle in a forward gear and attempt to drive forward.
With the key in the "on" or "battery charge" position, rapidly apply and release the foot brake.
Pump the brakes until the air pressure drops below 80 psi.
2. Before driving a vehicle with a dual air brake system, you should allow time for the air compressor to build up a minimum of ____ pressure in both the primary and secondary systems.
100 psi
50 psi
150 psi
35 psi
3. Before transporting sealed loads, you should check that:
the load can be inspected.
the load is properly secured.
the seal numbers match the placard numbers.
All of the above.
4. When driving a 60 foot truck at 35 mph in ideal conditions, you should keep at least _______ of space in front of you.
12 seconds
5 seconds
4 seconds
6 seconds
5. A driver distraction is anything that takes your attention away from driving, such as:
adjusting the radio.
All of the above.
6. Excessive use of the service brakes results in overheating. Too much heat can:
cause the brakes apply unevenly.
make the brakes stop working.
cause the brakes to squeak.
cause the brakes to grab.
7. To check the slack adjusters on S-cam brakes, you should:
park on level ground and fan off the air pressure by rapidly applying and releasing the foot brake.
park on level ground, chock the wheels and release the parking brakes, then use gloves and pull hard on each slack adjuster that you can reach.
release the parking brake valve and begin reducing the air pressure by stepping on and off the brake pedal.
All of the above.
8. Do NOT use the parking brakes:
if the brakes are very hot.
when you park for less than two hours.
when you leave your vehicle.
to test that they work.
9. In air-operated disc brakes, the pressure of the ______ on the ______ turns a "power screw".
slack adjuster; cam roller
brake camshaft; tie rod
brake chamber; slack adjuster
slack adjuster; tie rod
10. The __________ keeps air from going out if the air compressor develops a leak.
tractor protection valve
emergency relay valve
air compressor drive belt
one-way check valve
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DC 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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