Idaho CDL Air Brakes Practice Test (ID) 2

4.9 out of 5 (38 votes)
80% Passing score
20 Questions
4 Mistakes allowed
As you prepare for your commercial driver's license in Idaho, it's crucial to ensure you're fully equipped with the knowledge to handle air brakes. Our Idaho CDL air brake practice test is designed to provide an authentic experience that mirrors the real DMV test. This comprehensive test features 20 multiple-choice questions, covering essential topics such as components, operation, safety inspections, and stopping distance calculations. One key aspect of our Idaho practice driving test is its alignment with the latest driving laws and regulations. Updated for 2026, this test ensures you're studying the most relevant information, making it an excellent tool for your preparation. The Idaho CDL air brake test also includes critical details about dual air brake systems, which enhance safety by providing a backup in case one system fails. Visual learning aids are an integral part of our CDL air brakes practice test. Many questions are accompanied by images, which can be particularly beneficial for visual learners, helping you grasp complex concepts more effectively. This makes the Idaho DMV air brake test not only informative but also engaging. Driving in Idaho presents unique challenges that our Idaho DMV practice test takes into consideration. Whether you're navigating the rugged terrains of the Sawtooth Mountains or driving through the snowy conditions in winter, understanding the nuances of air brake systems is crucial. Our test is tailored to reflect these local driving conditions, ensuring you're well-prepared for any situation. To pass this Idaho CDL air brake test, you need to answer at least 16 questions correctly. This rigorous standard ensures that you have a solid understanding of air brake systems, which is essential for safe driving on Idaho's diverse roads. Whether you're a new driver or looking to renew your CDL, our Idaho practice drivers test is an ideal resource to ensure you're ready for the real test.
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Sample Idaho Air Brakes Test Questions

Question 1

During the applied air-leakage test, how much pressure may a single vehicle lose with the engine off and the service brake fully applied?

  1. A No more than 3 psi in one minute
  2. B No more than 2 psi in 45 seconds
  3. C No more than 1 psi in one minute
  4. D No more than 1 psi in 30 seconds

Correct answer: A – No more than 3 psi in one minute

The Idaho CDL manual sets the maximum applied leakage rate at three psi in one minute for a single vehicle. For a combination vehicle, the limit is four psi in one minute. Excessive pressure loss indicates a leak that must be corrected before the vehicle is driven.

Source: Idaho Commercial Driver’s License Manual — § 5.3.3, “Step 7 Final Air Brake Check”

Question 2

In an S-cam air brake, what function does the slack adjuster perform?

  1. A Regulates pressure inside the air tanks
  2. B Controls when the compressor cuts in
  3. C Removes free play from the brake pedal
  4. D Turns the brake camshaft as the chamber pushrod moves

Correct answer: D – Turns the brake camshaft as the chamber pushrod moves

Air entering the brake chamber pushes the rod outward. The rod moves the slack adjuster, which turns the brake camshaft and S-cam to press the shoes against the drum. Slack adjusters must also be inspected because excessive movement can indicate that the brake is out of adjustment.

Source: Idaho Commercial Driver’s License Manual — § 5.1.8, “Foundation Brakes”, Idaho Commercial Driver’s License Manual — § 5.3.2, “During Step 5 Walk-around Inspection”

Question 3

What force applies spring-type parking and emergency brakes when their air pressure is released?

  1. A Air pressure
  2. B Spring pressure
  3. C Hydraulic-fluid pressure
  4. D Engine vacuum

Correct answer: B – Spring pressure

Spring brakes use mechanical spring force to apply the brakes. During normal driving, air pressure compresses and holds back the powerful springs. Releasing or losing that air allows the springs to apply the parking or emergency brakes.

Source: Idaho Commercial Driver’s License Manual — § 5.1.14, “Spring Brakes”

Question 4

Why should you avoid rapidly pumping or “fanning” the air-brake pedal during normal braking?

  1. A It prevents the compressor from operating
  2. B It increases the pressure stored in the tanks
  3. C It can release air faster than the compressor replaces it
  4. D It automatically applies the parking brakes

Correct answer: C – It can release air faster than the compressor replaces it

The Idaho CDL manual warns that pressing and releasing the brake pedal unnecessarily can reduce tank pressure faster than the compressor can restore it. If pressure becomes too low, braking ability is reduced and the spring brakes may apply. On downgrades, select a proper low gear and use the recommended controlled braking technique.

Source: Idaho Commercial Driver’s License Manual — § 5.1.7, “The Brake Pedal”; § 5.4.6, “Proper Braking Technique”

Question 5

How should a vehicle be secured before checking manual slack-adjuster movement by hand?

  1. A Apply the service brakes and leave the engine running
  2. B Drain every air tank and remove the wheel chocks
  3. C Park level, chock the wheels, and release the parking brakes
  4. D Apply the emergency brakes and place the transmission in gear

Correct answer: C – Park level, chock the wheels, and release the parking brakes

Park on level ground and chock the wheels before releasing the parking brakes. Wearing gloves, pull hard on each reachable slack adjuster. Movement of more than about one inch where the pushrod attaches probably indicates that the brake needs adjustment or repair.

Source: Idaho Commercial Driver’s License Manual — § 5.3.2, “During Step 5 Walk-around Inspection”

Question 6

While an air-brake vehicle is being driven, what normally keeps its spring brakes released?

  1. A Mechanical clamps
  2. B Wheel rotation
  3. C Spring pressure
  4. D Air pressure

Correct answer: D – Air pressure

Powerful springs provide the force that applies spring brakes, but air pressure holds those springs back during normal driving. When the driver operates the parking-brake control, air is released and the springs apply the brakes. A major loss of system pressure can produce the same result.

Source: Idaho Commercial Driver’s License Manual — § 5.1.14, “Spring Brakes”

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