PracticeVideosBlogFlashcardsEspañol
All Practice Exams

Free Practice Questions for MO CDL Air Brakes

Exam-style questions and explanations by OpenExamPrep.

✓ No registration✓ No credit card
220+ Questions
100% Free

Loading practice questions...

Same family resources

Explore More CDL Air Brakes Knowledge Test

Continue into nearby exams from the same family. Each card keeps practice questions, study guides, flashcards, videos, and articles in one place.

Alabama CDL Air Brakes Knowledge Test

Practice QuestionsNational Study Guide7 Job Wiki

Arkansas CDL Air Brakes Knowledge Test

Practice QuestionsNational Study Guide7 Job Wiki

California CDL Air Brakes Knowledge Test

Practice QuestionsNational Study Guide7 Job Wiki

Colorado CDL Air Brakes Knowledge Test

Practice QuestionsNational Study Guide7 Job Wiki

Florida CDL Air Brakes Knowledge Test

Practice QuestionsNational Study Guide7 Job Wiki

Georgia CDL Air Brakes Knowledge Test

Practice QuestionsNational Study Guide7 Job Wiki
Exam Review

Key Facts: MO CDL Air Brakes Exam

25

Questions on the Air Brake Written Exam

Missouri CDL Manual, Section 14

80%

Passing Score

49 CFR 383.135 / Missouri DOR

L Restriction

Air Brakes Prohibition Code

49 CFR 383.95 / Missouri DOR

100 / 120-140 psi

Governor Cut-In / Cut-Out Pressure

Missouri CDL Manual Sections 5.1.2 and 11.1.2

55 psi

Low Air Warning Must Come On Before

Missouri CDL Manual Section 5.1.11

20 to 45 psi

Spring Brake Pop-Out Range

Missouri CDL Manual Section 5.1

Missouri's CDL Air Brake written test has 25 multiple-choice questions, requires 80% (20 correct), and is given in English only under § 302.720.2(1) RSMo. Passing it and the skills test in an air-brake vehicle avoids the L restriction. Key Missouri manual figures: governor cut-in about 100 psi and cut-out about 125 psi, a low-air warning before pressure falls below 55 psi, spring brakes at 20-45 psi, and static air loss under 2 psi per minute for a single vehicle.

Sample MO CDL Air Brakes Practice Questions

Try these sample questions to review concepts for the MO CDL Air Brakes exam. Each question includes a detailed explanation. Start the interactive quiz above for the full 220+ question experience with AI tutoring.

1Which commercial license restriction is placed on a Missouri driver's license if the applicant fails or does not take the Air Brakes written knowledge test?
A.L: no CMV with air brakes
B.E: no CMV with a manual transmission
C.M: no Class A passenger vehicle
D.O: no tractor-trailer connected by a fifth wheel
Explanation: Under 49 CFR 383.95(a), if an applicant fails the air brake knowledge test or takes the skills test in a vehicle without air brakes, the license is restricted from operating any CMV with air brakes. Section 14 of the Missouri CDL Manual calls this the L restriction (Non-Airbrake CMV); to avoid it, pass the written air brake test and the skills test in a vehicle with air brakes.
2What is the difference between the 'L' restriction and the 'Z' restriction on a Missouri CDL?
A.The 'L' restriction applies to buses only; the 'Z' restriction applies to tractor-trailers
B.L bars any air-brake CMV; Z bars full air brakes after testing with air-over-hydraulic
C.The 'L' restriction is temporary for 30 days; the 'Z' restriction is permanent
D.Both restrictions are identical and can be used interchangeably by state examiners
Explanation: Under 49 CFR 383.95, an 'L' restriction bans operating any vehicle equipped with any type of air brakes. A 'Z' restriction is placed when an applicant tests in a vehicle with an air-over-hydraulic system, barring them from full air brake vehicles.
3Under § 302.720.2(1) RSMo, what language restriction governs the administration of the Air Brakes CDL written test in Missouri?
A.Applicants may use foreign-language translation dictionaries
B.The test may be given in English, Spanish, or French at the applicant's request
C.English only, with no translators or interpreters
D.Applicants may request the test in another language at least 30 days in advance
Explanation: Pursuant to § 302.720.2(1) RSMo, all CDL written examinations in Missouri must only be administered in English, and no translators or interpreters are permitted in the testing room.
4What is required for a Missouri commercial driver to remove the 'L' restriction from their commercial license?
A.Pay an administrative removal fee at a local license office without testing
B.Submit an employer letter stating the driver understands air brake principles
C.Complete 50 hours of unverified driving time in an air-brake vehicle
D.Pass the air brake knowledge test and the skills test in a full air-brake vehicle
Explanation: Section 14 of the Missouri CDL Manual says that to avoid the L restriction you must pass the written air brake test and the skills test in a vehicle equipped with air brakes. Testing in a vehicle with air-over-hydraulic brakes instead results in the Z restriction (no full air brake CMV).
5During the Missouri CDL vehicle inspection test in an air-brake vehicle, what happens if you do not correctly explain and demonstrate all parts of the air brake check?
A.It is an automatic failure of the CDL vehicle inspection test
B.The examiner deducts points but lets you finish the inspection
C.You may repeat any missed part once before it is scored
D.The examiner skips the air brake check if the rest of the inspection is perfect
Explanation: Section 11.1.2 of the Missouri CDL Manual says failure to explain and demonstrate all four parts of the air brake check correctly (governor cut-out, leakage rate, low-air warning, and spring brake/parking brake valve activation) results in an automatic failure of the CDL vehicle inspection test.
6Missouri's Air Brake written exam has 25 questions, and Section 14 of the Missouri CDL Manual requires 80% on each exam. How many correct answers do you need to pass?
A.19
B.20
C.21
D.22
Explanation: Eighty percent of 25 is 20 (0.80 x 25 = 20). The manual's exam table lists the Air Brake exam at 25 questions and says you must score 80% on each exam, which matches the federal standard in 49 CFR 383.135.
7Which agency is responsible for administering the CDL Air Brakes written knowledge test and skills test in Missouri?
A.Federal Highway Administration regional offices
B.Missouri Department of Natural Resources
C.The Missouri State Highway Patrol
D.City municipal traffic divisions
Explanation: Missouri CDL written tests, including the Air Brake test, are given at Missouri State Highway Patrol driver examination stations, and skills tests are given by appointment at MSHP CDL test sites; a certified Missouri third-party tester may also give the skills test. Department of Revenue license offices issue the CLP or CDL.
8Under 49 CFR 393.53, automatic brake adjusters are required on air-braked commercial motor vehicles manufactured on or after which date?
A.October 20, 1993
B.January 1, 2020
C.September 1, 2010
D.October 20, 1994
Explanation: 49 CFR 393.53(b) requires automatic brake adjusters on CMVs with air brakes manufactured on or after October 20, 1994; the October 20, 1993 date in 393.53(a) applies to hydraulic brakes. Section 5.3.2 of the Missouri CDL Manual puts it simply: all vehicles built since 1994 have automatic slack adjusters, and they must still be checked.
9According to Section 14 of the Missouri CDL Manual, a driver with the L restriction is not allowed to operate which vehicles?
A.Any CMV with air brakes, including air-over-hydraulic systems
B.Only full-air-brake CMVs; air-over-hydraulic is allowed
C.Only combination vehicles with air brakes
D.Only air-braked vehicles that carry passengers
Explanation: Section 14 says an L-restricted driver may not drive a CMV with air brakes and is also prohibited from operating a vehicle with an air-over-hydraulic brake system. Under 49 CFR 383.95(a)(2), air brakes include any system operating fully or partially on the air brake principle.
10Under 49 CFR 393.55, antilock braking systems have been required on newly built air-braked truck tractors since which date?
A.January 1, 1985
B.March 1, 1997
C.June 15, 2005
D.January 1, 2018
Explanation: 49 CFR 393.55(c) requires ABS on truck tractors with air brakes manufactured on or after March 1, 1997, and on other air-braked CMVs (trucks, buses, trailers, and converter dollies) built on or after March 1, 1998. Section 5.1.16 of the Missouri CDL Manual gives the same dates.

About the MO CDL Air Brakes Exam

The Missouri CDL Air Brakes Knowledge Test is the 25-question written test required for commercial drivers who operate vehicles with air brakes. Passing it and the skills test in an air-brake vehicle avoids or removes the L restriction. Independent practice by OpenExamPrep covers Section 5 of the Missouri CDL Manual: system parts, dual air systems, air brake inspection, stopping technique, and emergencies. These practice questions are a study aid, not an official-format simulation.

Exam sponsor: Missouri Department of Revenue (DOR) and Missouri State Highway Patrol (MSHP). The requirements and fees below concern the certification or admission exam, separate from our free practice resources.

Assessment

A 25-question multiple-choice knowledge test given in English only by the Missouri State Highway Patrol under § 302.720.2(1) RSMo. To drive air-brake CMVs without the L restriction, applicants must also pass the skills test in a vehicle with air brakes, including the four-part air brake check.

Time Limit

No time limit published; the Missouri CDL Manual says written CDL testing can take 1-2 hours depending on how many tests you take

Passing Score

80% on each CDL knowledge test

Exam / Certification Fees

$25 per written or driving test (§ 302.720 RSMo); first CLP $44 total; most first-time CDLs about $83 with the skills test fee

Exam sponsor website

Fees, eligibility, and exam policies can change. Confirm them with the exam sponsor before applying or paying.

Official sources

Our practice resources: topics covered

We aim to reflect publicly available exam outlines and topic information in our study resources. Coverage, format, and difficulty may differ from the actual exam, and we cannot guarantee that every detail is accurate or current. Confirm exam requirements, fees, and policies with the official exam sponsor.

Manual Section 1 & Section 5 introduction (official weight not published)

Missouri Air Brake Regulations and Restrictions

The L restriction (no CMV with air brakes), the Z restriction (air-over-hydraulic), ELDT rules, English-only testing under § 302.720.2(1) RSMo, and MSHP testing procedures.

Manual Section 5.1 (official weight not published)

Parts of an Air Brake System

Air compressor, governor cut-in (about 100 psi) and cut-out (about 125 psi; 120-140 psi in the air brake check), air tanks and drains, alcohol evaporator, safety valve (150 psi), brake pedal, S-cam, wedge, and disc brakes, gauges, and spring brakes.

Manual Section 5.2 (official weight not published)

Dual Air Brake Systems

Primary and secondary systems, building at least 100 psi in both before driving, a low-air warning that must come on before 55 psi in either system, and what happens if one system fails.

Manual Section 5.3 (official weight not published)

Inspecting Air Brake Systems

Slack adjuster and drum checks, governor cut-in and cut-out checks, static leakage (under 2 psi/min single, 3 combination), applied leakage (3 and 4 psi/min), low-air warning before 55 psi, spring brake pop-out (20-45 psi), pressure build-up (85 to 100 psi within 45 seconds), and parking and service brake tests.

Manual Section 5.4 (official weight not published)

Using Air Brakes and Stopping Techniques

Normal stopping, brake lag distance, total stopping distance, brake application pressure, mountain downgrades, engine braking, heat buildup, and brake fade.

Manual Section 5.4.3 & 5.4.4 (official weight not published)

Emergency Braking and Brake Failure

Controlled braking versus stab braking, low air pressure emergency response, runaway vehicle escape ramps, parking brake application, and antilock braking systems (ABS).

Preparing for the MO CDL Air Brakes Exam

What You Need to Know

  • Passing score: 80% on each CDL knowledge test
  • Assessment: A 25-question multiple-choice knowledge test given in English only by the Missouri State Highway Patrol under § 302.720.2(1) RSMo. To drive air-brake CMVs without the L restriction, applicants must also pass the skills test in a vehicle with air brakes, including the four-part air brake check.
  • Time limit: No time limit published; the Missouri CDL Manual says written CDL testing can take 1-2 hours depending on how many tests you take
  • Exam / certification fees: $25 per written or driving test (§ 302.720 RSMo); first CLP $44 total; most first-time CDLs about $83 with the skills test fee Official sources

Using Our Practice Resources

  • Work through all 220 available questions
  • Review every answer and explanation
  • Track weak areas and revisit them
  • Use our AI tutor for tough concepts

Frequently Asked Questions

How many questions are on the Missouri CDL Air Brake test?

Section 14 of the Missouri CDL Manual lists the Air Brake written exam at 25 multiple-choice questions. You must score 80%, which is 20 correct.

What is the Missouri 'L' restriction on a CDL?

The L restriction restricts a commercial driver from operating any commercial motor vehicle equipped with air brakes. It is placed on the license if the driver fails or does not take the Air Brakes knowledge test, or takes the skills test in a vehicle without air brakes.

What is the difference between the 'L' and 'Z' restrictions in Missouri?

The L restriction prohibits operating any vehicle with air brakes. The Z restriction occurs when a driver tests in a vehicle equipped with an air-over-hydraulic brake system, prohibiting the driver from operating CMVs with full air brakes.

What are the acceptable air leakage rates during an inspection?

With the engine off and the parking brake released, the loss rate should be less than 2 psi in one minute for a single vehicle and less than 3 psi for a combination. With the foot brake fully applied, the loss should be no more than 3 psi in one minute for a single vehicle and 4 psi for a combination (Missouri CDL Manual Sections 5.3 and 11).

At what air pressure must the low air warning activate?

Section 5.1.11 of the Missouri CDL Manual says the low air warning must come on before tank pressure falls below 55 psi (or one-half the governor cut-out pressure on older vehicles). On large buses it is common for the warning to signal at 80-85 psi.