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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 Iowa CDL knowledge test. The IA 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 Iowa CDL Manual. Take this IA CDL practice test now to prepare for the actual air brakes test!
1. With brake drums, if brakes become too hot:
the brakes may stop working.
your ABS will malfunction.
the brakes will supply too much power to the drive wheels.
2. The air storage tanks:
stop the compressor from pumping air.
are used to hold compressed air.
are connected to the engine through gears or a v-belt.
3. You are driving on a steep downgrade. If your safe speed is 35 mph, you should apply the brakes when your speed reaches:
35 mph
25 mph
30 mph
4. If air pressure does not build up fast enough:
you should turn the electrical power on and step on and off the brake pedal.
the pressure may drop too low during driving.
you should put the parking brake on and gently pull against it in a low gear.
5. Before driving a truck or bus with a dual air brake system, the minimum pressure in both the primary and secondary systems should be at least:
100 psi.
130 psi.
75 psi.
6. If your vehicle is equipped with air brakes, loss of air pressure in the emergency line causes:
the speed of your vehicle to increase.
the trailer emergency brakes to come on.
the trailer spring brakes to come on.
7. The safety valve is usually set to open at:
150 psi.
100 psi.
200 psi.
8. The air brake lag distance at 55 mph on dry pavement adds about:
32 feet.
75 feet.
60 feet.
9. When parking a trailer without spring brakes, it is very important for safety that you use wheel chocks. Why?
You may not notice a major leak in the service line until you try to put the brakes on.
if you don't use wheel chocks, supply air will be sent to the service line instead of going to charge the trailer air tanks.
The air could leak out of the trailer air tank, releasing its emergency brakes.
10. A broken exhaust system:
poses no threat to the driver.
can let poisonous carbon monoxide to leak into the cab.
can improve fuel efficiency.
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IA 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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