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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. With brake drums, if brakes become too hot:
the brakes will supply too much power to the drive wheels.
the air compressor will kick on to cool the brakes.
your ABS will malfunction.
the brakes may stop working.
2. If the ABS is not working:
you still have normal brake functions.
the vehicle will have no brakes.
the vehicle will have weak brakes.
None of the above.
3. Which of the following is NOT a way to determine if your trailer is equipped with ABS (antilock braking system)?
It has yellow ABS malfunction lamps.
The letters "ABS" are printed on the side of the steering wheel.
Wheel speed sensor wires are coming from the back of the brakes.
It was built after March 1, 1998.
4. The air compressor governor controls:
the air pressure applied to the brakes.
when the air compressor will pump air into the air storage tanks.
when air tank pressure falls below the “cut-out” level.
the speed of the air compressor.
5. If your vehicle is equipped with a front brake limiting valve, to ensure normal stopping power make sure the control is:
in the "neutral" position.
in the "slippery" position.
in the "off" position.
in the "normal" position.
6. If the air tanks are not drained:
the water can freeze in cold weather and cause brake failure.
the air pressure in the tanks is reduced.
your speed must be reduced to 5 MPH below your “safe” speed.
the spring brakes will come on.
7. Pressing and releasing the brake pedal unnecessarily can:
causes all the air to be lost.
apply more air pressure.
let air out faster than the compressor can replace it.
causes friction, which slows the vehicle.
8. If air doesn't flow all the way to the back:
your lower fifth wheel may fall off.
a rollover is more likely.
your brakes will not work properly.
the trailer will tend to swing around.
9. The low pressure warning signal will generally activate when the air pressure falls between:
30–35 psi.
85–100 psi.
55–75 psi.
80–85 psi.
10. If an aggressive driver is involved in an accident down the road, you should:
confront the aggressive driver.
stop a safe distance from the accident scene, wait for the police and report the behavior you witnessed.
try to get their vehicle to the side of the road.
make eye contact with the driver.
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DC 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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