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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 Idaho CDL knowledge test. The ID 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 Idaho CDL Manual. Take this ID CDL practice test now to prepare for the actual air brakes test!
1. When the air pressure is built up to governor cutoff, the air leakage rate for combination vehicles with the engine off and the foot brake fully applied should be less than_____ in one minute.
3 psi
4 psi
2 psi
2. The one-way check valve:
supplies air to the trailer air tanks.
keeps air from going out if the air compressor develops a leak.
keeps your wheels from locking up when you brake hard.
3. Controlled braking:
can be used to keep your vehicle in a straight line and allow you to turn if necessary.
must be used when you need to turn sharply while braking.
involves locking the wheels and then releasing the brakes.
4. What factors can cause brakes to fade or fail?
Not pressing the brake pedal hard enough.
Overheating, low air pressure or water in the air tanks.
Going too slow.
5. To prevent rollover, you should:
place the cargo near the rear of the trailer.
keep the cargo as close to the ground as possible.
put the lightest parts of the cargo under the heaviest parts.
6. Older trailers do not have spring brakes. If the air supply leaks away:
there will be no emergency brakes.
the trailer will stop normally.
the ABS won't work properly.
7. If the air tanks are not drained:
your speed must be reduced to 5 MPH below your “safe” speed.
the air pressure in the tanks is reduced.
the water can freeze in cold weather and cause brake failure.
8. Which of the following is not a way to know when to change gears?
Check that the pressure gauge shows normal oil pressure
Use engine speed (rpm)
Use road speed (mph)
9. You are driving a vehicle with air brakes when the low air pressure warning light and buzzer come on. You should:
activate your hazard lights and drive to the nearest place where you can stop.
slow down and test your brakes.
pull off the road and stop immediately.
10. The safety relief valve is usually set to open at ____ psi.
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ID Air Brakes Test

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