Missouri CDL Air Brakes Practice Test (MO) 2

5 out of 5 (38 votes)
80% Passing score
20 Questions
4 Mistakes allowed
Are you gearing up for your commercial driver's license air brakes endorsement in Missouri? Look no further! Our Missouri permit practice test is designed specifically to help you pass with flying colors. With 20 multiple-choice questions, this test covers critical topics such as the components and operation of air brake systems, safety inspections, and stopping distance calculations. You'll also delve into the specifics of dual air brake systems, which are vital for maintaining safety on the road by providing a backup in case one system fails. To succeed, you'll need to correctly answer 16 out of the 20 questions, ensuring you're well-prepared for the real Missouri CDL air brake test. Our Missouri drivers license practice test is available online 24/7, allowing you to study at your own pace and on your own schedule. This flexibility is particularly beneficial for busy Missourians who juggle various responsibilities. Whether you're a farmer navigating the rural roads of the Ozarks, a trucker hauling goods along I-70, or a commuter braving the traffic in St. Louis, this permit test practice is tailored to fit your needs. Remember, obtaining a commercial driver's license requires you to pass not just the Missouri CDL air brake practice test but also the general knowledge test. We've got you covered there too, with a range of prep tests available to help you ace every aspect of your CDL test. Since driving laws can differ from state to state, our Missouri DMV practice test is customized to reflect the specific regulations, rules, and road signs you'll encounter in Missouri. This state-specific focus ensures that you're not only preparing for the test but also gaining knowledge that will be directly applicable when you're out on the road in Missouri. From understanding the nuances of driving through Missouri's varied terrains to adhering to local traffic laws, our CDL air brakes practice test prepares you for all the challenges you might face. By focusing on the specifics of the MO air brakes CDL test, we ensure that you're studying the material that matters most. So, whether you're practicing from the comfort of your home in Kansas City or during a break at a truck stop, our Missouri CDL air brake practice test is your reliable companion on the road to obtaining your CDL air brakes endorsement.
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Sample Missouri Air Brakes Test Questions

Question 1

During a sudden emergency stop, how should you brake?

  1. A Apply the trailer hand valve before using the service brakes
  2. B Keep the vehicle straight while maintaining steering control
  3. C Lock the wheels and keep them locked until stopped
  4. D Turn sharply while applying maximum brake pressure

Correct answer: B – Keep the vehicle straight while maintaining steering control

The Missouri manual instructs drivers to brake in a way that keeps the vehicle straight while allowing them to steer if necessary. Controlled braking applies maximum pressure without locking the wheels; stab braking releases the brakes after lockup and reapplies them once the wheels roll. With working ABS on all axles, the brakes may be fully applied during an emergency stop.

Source: Missouri Commercial Driver License Manual — §§ 5.4.2–5.4.3, “Braking with Antilock Brakes” and “Emergency Stops”

Question 2

With the engine off and brakes released, a combination vehicle's air pressure should drop by less than how many psi in one minute?

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

Correct answer: B – 3 psi

Begin this leakage test with a fully charged air system, turn off the engine, and release the parking brakes. During the one-minute test, a combination vehicle should lose less than three psi. A single vehicle should lose less than two psi during the same released-brake test. Excessive pressure loss indicates an air leak that must be corrected before driving.

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

Question 3

What is the function of a slack adjuster in an S-cam brake?

  1. A It regulates pressure inside the air tanks
  2. B It controls when the spring brakes apply
  3. C It removes free play from the brake pedal
  4. D It transfers pushrod movement to the camshaft and maintains brake adjustment

Correct answer: D – It transfers pushrod movement to the camshaft and maintains brake adjustment

In an S-cam brake, air pressure extends the chamber pushrod, moving the slack adjuster and twisting the brake camshaft. Automatic slack adjusters help maintain proper brake adjustment during operation. The Missouri manual also requires drivers to check accessible adjusters because excessive movement may indicate an adjustment or mechanical problem. They do not regulate air-tank pressure.

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

Question 4

With the engine off and service brakes fully applied, what is the maximum one-minute air-pressure drop for a single vehicle such as a straight truck or bus?

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

Correct answer: A – 3 psi

Build the system to governor cutoff, shut off the engine, release the parking brake, and hold the foot brake fully applied for one minute. A single vehicle must not lose more than three psi during that period. For comparison, the corresponding limit for a combination vehicle is four psi. A greater loss indicates excessive leakage that must be repaired before driving.

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

Question 5

Which substance is the intended working medium in an air-brake system?

  1. A Water
  2. B Compressed air
  3. C Compressor oil
  4. D A mixture of air, water, and oil

Correct answer: B – Compressed air

Compressed air operates the brake system. Water and compressor oil may enter with the compressed air, but the Missouri manual identifies both as harmful to the system. They collect at the bottom of the storage tanks and must be removed through the drain valves. Water is especially dangerous because it can freeze and interfere with brake operation.

Source: Missouri Commercial Driver License Manual — §§ 5.1.3–5.1.4, “Air Storage Tanks” and “Air Tank Drains”

Question 6

A supply pressure gauge measures the amount of time remaining before an S-cam rotates.

  1. A True
  2. B False

Correct answer: B – False

A supply pressure gauge shows the amount of air pressure in the storage tank or tanks. A dual air-brake system may have two gauges or one gauge with two needles. The gauge does not measure S-cam timing. The S-cam rotates mechanically when air pressure moves the brake-chamber pushrod and slack adjuster.

Source: Missouri Commercial Driver License Manual — §§ 5.1.8–5.1.9, “Foundation Brakes” and “Supply Pressure Gauges”

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