North Dakota CDL — Air Brakes practice
North Dakota CDL — Air Brakes: Safe Driving Practices practice test
Following distance, scanning, blind spots, using your lights, and the habits that prevent crashes and keep you in control.
Content reviewed against official driver handbooks · August 12, 2026
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12 sample Safe Driving Practices questions with the correct answer, a short explanation, and the official handbook reference. Read through them, then take the quiz above.
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1. The manual cites the National Transportation Safety Board on manually adjusting automatic slack adjusters. Why does the Board call the practice dangerous?
Correct answer: It leaves the operator falsely confident that the brakes are effective
The manual gives the Board's view that the practice creates a false sense of security regarding how well the brakes work. The adjustment hides a mechanical problem without fixing it, so the brake is likely to go back out of adjustment.
Source: North Dakota Commercial Driver License Manual — Section 5.3.2, During Step 5 Walkaround Inspection
2. Your air brake system has an alcohol evaporator. During cold weather, how often does the manual say to check the alcohol container and fill it as needed?
Correct answer: Every day
The evaporator puts alcohol into the air system to cut the risk of ice in valves and other parts. The manual says to look at the container and top it up daily while the weather is cold.
Source: North Dakota Commercial Driver License Manual — Section 5.1.5, Alcohol Evaporator
3. You release the brake pedal on a vehicle with s-cam brakes, and the s-cam rotates back. What draws the brake shoes back off the drum?
Correct answer: A spring
When the pedal is released, the s-cam turns back and a spring pulls the shoes clear of the drum so the wheels turn freely again.
Source: North Dakota Commercial Driver License Manual — Section 5.1.8, Foundation Brakes
4. Compressed air usually carries some water and compressor oil. Where does the manual say they tend to collect, and what is fitted there?
Correct answer: In the bottom of the air tank, where each tank has a drain valve
Water and oil settle at the bottom of the tanks, so every tank has a drain valve there. The manual warns that in cold weather this water can freeze and lead to brake failure, so the tanks need to be drained completely.
Source: North Dakota Commercial Driver License Manual — Section 5.1.4, Air Tank Drains
5. Braking creates friction and heat at the drum. What does the manual say determines how much heat a drum can take without damage?
Correct answer: How hard the brakes are applied and for how long
The shoes and linings press against the inside of the drum, and the friction makes heat. The manual ties a drum's heat tolerance to the force and the duration of braking, and warns that brakes can quit working if they get too hot.
Source: North Dakota Commercial Driver License Manual — Section 5.1.8, Foundation Brakes
6. You are about to test the low pressure warning signal in the Step 7 final air brake check. How does the manual have you set things up before stepping on and off the brake pedal?
Correct answer: Engine off, electrical power on, and enough pressure that the warning is not on
You shut the engine off while there is enough air that the warning is not showing, switch the electrical power on, and then pump the pedal to bring tank pressure down. In North Dakota's Section 5 the signal has to come on before the tank falls under 60 psi.
Source: North Dakota Commercial Driver License Manual — Section 5.3.3, Step 7 Final Airbrake Check
7. Which of these is NOT one of the three braking systems that the manual says make up air brakes?
Correct answer: The retarder brake system
The manual describes air brakes as three systems: the service brake, the parking brake and the emergency brake. A retarder is not on that list.
Source: North Dakota Commercial Driver License Manual — Section 5, Airbrakes
8. Outside of brake maintenance and adjuster installation, when does the manual accept manually adjusting an automatic slack adjuster?
Correct answer: Only as a temporary measure in an emergency
The manual treats a manual adjustment as a stopgap for an emergency, because the brake will probably be out of adjustment again soon; the underlying problem is still there. The manual recommends getting the vehicle to a repair shop promptly.
Source: North Dakota Commercial Driver License Manual — Section 5.3.2, During Step 5 Walkaround Inspection
9. Your tractor has a dual air brake system and is hooked to a trailer. Which of the two systems does the manual say supplies air to the trailer?
Correct answer: Both systems
The manual says the primary and the secondary system both feed air to the trailer when there is one.
Source: North Dakota Commercial Driver License Manual — Section 5.2, Dual Airbrake
10. The manual gives a separate air pressure buildup standard for single air systems on pre-1975 vehicles. Which matches its typical requirement?
Correct answer: 50 psi up to 90 psi in 3 minutes, at idle speed
For single air systems the typical requirement is a climb from 50 psi up to 90 psi in no more than three minutes with the engine idling at 600 to 900 rpm. The figure of 85 to 100 psi in 45 seconds belongs to dual air systems at operating rpm.
Source: North Dakota Commercial Driver License Manual — Section 5.3.3, Step 7 Final Airbrake Check
11. The Air Brakes section adds a check to the engine compartment step of the seven-step inspection. If the air compressor is belt-driven, what do you check?
Correct answer: The condition and tightness of the drive belt
During Step 2, the engine compartment check, a belt-driven compressor's belt is checked for tightness and should be in good condition.
Source: North Dakota Commercial Driver License Manual — Section 5.3.1, During Step 2 Engine Compartment Checks
12. North Dakota's air leakage test first times the pressure drop with the parking brake released. For the second part, how much pressure does the manual say to apply with the brake pedal?
Correct answer: 90 psi or more
After the first timing, the pedal application should be at least 90 psi. Once the initial drop is over, losing over three psi a minute in a single vehicle, or over four psi in a combination, is too much, and the leak has to be found and fixed before the vehicle is driven.
Source: North Dakota Commercial Driver License Manual — Section 5.3.3, Step 7 Final Airbrake Check
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Every North Dakota question is written from the official North Dakota driver handbook and checked against its current edition. DMV Test Free is a free, independent study resource — not affiliated with any DMV or government agency. About DMV Test Free