North Carolina CDL Air Brake Test (NC) 2026

4.9 out of 5 (81 votes)
80% Passing score
20 Questions
4 Mistakes allowed
Are you preparing for your NC CDL air brakes endorsement? Look no further! Our NC CDL air brakes practice test offers a comprehensive and engaging way to master all aspects of air brake systems. This DMV practice test features 20 multiple-choice questions meticulously crafted to cover essential components like compressors, reservoirs, and brake chambers. Additionally, you will delve into the operational principles and crucial safety protocols necessary for effective air brake usage. One of the unique aspects of air brakes is the brake lag time, which is vital for drivers to understand when calculating stopping distances. Our North Carolina permit test includes questions that address this critical component, ensuring you are well-prepared for real-world driving scenarios. To achieve a passing score, you must correctly answer at least 16 questions, demonstrating your proficiency in air brake systems and readiness for the NC air brakes CDL test. Visual learning aids are a standout feature of our DMV practice test. Many of the sample questions come with images to help you visualize and better understand the concepts. This is particularly beneficial for visual learners, making the learning process more interactive and effective. Unlike many paid practice tests, our NC permit test is completely free. You get access to the same high-quality study opportunities without any cost, providing an affordable way to prepare for your CDL air brake test. The questions in our North Carolina CDL air brakes practice test are based on the official NC Driver's Manual. This ensures that the content is accurate and relevant, mirroring the topics covered in the actual DMV air brake test. If it's in the manual, it's on our test, so you can be confident that you're studying the right material. Get started with our NC CDL air brakes practice test today and ensure you're fully prepared for your commercial driver's license air brakes endorsement. With our free, comprehensive, and visually aided North Carolina driving test practice, you'll master the fundamentals of safe and effective air brake operation.
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Sample North Carolina Air Brakes Test Questions

Question 1

Under good conditions, an air-braked commercial vehicle traveling at 55 mph can stop in about 100 feet.

  1. A. True
  2. B. False

Correct answer: B. – False

The North Carolina CDL manual estimates a total stopping distance of more than 450 feet at 55 mph for an average driver under good traction and brake conditions. Air brakes add brake lag while compressed air travels through the system. At 55 mph on dry pavement, that lag alone adds about 32 feet to the stopping distance.

Source: North Carolina Commercial Driver License Manual — § 5.4.4, “Stopping Distance”

Question 2

During a North Carolina air-brake check, the engine is off and the service brake is fully applied. What is the maximum one-minute pressure loss for a single vehicle?

  1. A. 3 psi
  2. B. 2 psi
  3. C. 4 psi
  4. D. 5 psi

Correct answer: A. – 3 psi

With air pressure at governor cutoff, the engine off, parking brake released, and foot brake fully applied, a single vehicle must not lose more than 3 psi in one minute. The corresponding limit for a combination vehicle is 4 psi. Excessive leakage must be located and repaired before the vehicle is driven.

Source: North Carolina Commercial Driver License Manual — § 5.3.3, “Step 7 Final Air Brake Check”

Question 3

What is the function of an automatic slack adjuster in an air-brake system?

  1. A. Regulate pressure in the air reservoirs
  2. B. Control when the spring brakes apply
  3. C. Remove free play from the brake pedal
  4. D. Compensate for brake wear and maintain proper foundation-brake adjustment

Correct answer: D. – Compensate for brake wear and maintain proper foundation-brake adjustment

In an S-cam brake, the brake-chamber pushrod moves the slack adjuster, which rotates the brake camshaft. Automatic slack adjusters compensate for brake wear during full brake applications, but they still must be inspected. Excessive pushrod stroke can indicate a problem with the adjuster, its installation, or another foundation-brake component.

Source: North Carolina Commercial Driver License Manual — § 5.1.8, “Foundation Brakes”; § 5.3.2, “During Step 5 Walk-around Inspection”

Question 4

Which condition can reduce the effectiveness of both the service brakes and the spring parking/emergency brakes?

  1. A. Low hydraulic fluid in a vehicle with air-only brakes
  2. B. Brakes that are out of adjustment
  3. C. A burned-out clearance lamp
  4. D. Air pressure at normal governor cutout

Correct answer: B. – Brakes that are out of adjustment

Spring-brake effectiveness depends on the foundation brakes being properly adjusted. If the brakes are out of adjustment, the regular service brakes and the emergency or parking brakes will not work correctly. Poor adjustment can also force the remaining brakes to work harder, increasing the risk of overheating and brake fade.

Source: North Carolina Commercial Driver License Manual — § 5.1.14, “Spring Brakes”; § 5.4.5, “Brake Fading or Failure”

Question 5

In an air-brake system, what is a “wig wag”?

  1. A. A mechanical arm that drops into view as a low-air-pressure warning
  2. B. A lever that manually adjusts the service brakes
  3. C. A switch that activates the brake lights
  4. D. A valve that drains moisture from the air tanks

Correct answer: A. – A mechanical arm that drops into view as a low-air-pressure warning

A wig wag is a mechanical low-air-pressure warning device. The North Carolina CDL manual describes an arm that drops into the driver’s view when system pressure enters the low-pressure range. An automatic version rises out of view when adequate pressure is restored, while a manual-reset type must be repositioned by the driver after pressure recovers.

Source: North Carolina Commercial Driver License Manual — § 5.1.11, “Low Air Pressure Warning”

Question 6

On most large air-braked vehicles, spring brakes serve which functions?

  1. A. Parking only
  2. B. Normal service braking only
  3. C. Parking and emergency braking
  4. D. Routine speed control on downgrades

Correct answer: C. – Parking and emergency braking

North Carolina’s CDL manual explains that trucks, truck tractors, and buses need mechanically held parking and emergency brakes because air pressure can eventually leak away. Spring brakes commonly perform both functions. Air pressure holds the springs back during normal driving; releasing or losing that pressure allows the springs to apply the brakes.

Source: North Carolina Commercial Driver License Manual — § 5.1.14, “Spring Brakes”

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