- Updated for March 2025
- Based on 2025 MO commercial driver's license manual
Free Missouri CDL Air Brakes Test 2025
Securing a CDL without an air brake restriction is vital for expanded job opportunities in Missouri because most semi-trucks, tractor-trailers, and large buses rely on air brakes for safe navigation. Failure to pass the Missouri DOR CDL Air Brakes Knowledge Test results in your CDL including the restriction “L,” which will prevent you from operating commercial motor vehicles (CMVs) with air brakes. Failing the air brakes test in Missouri also results in a one-day waiting period and a retest fee should you decide to retake the test. Our Missouri DOR CDL Air Brakes Practice Tests help you pass your knowledge exam on the first attempt.
From the rolling hills, river valleys, and flat plains to the steep grades and winding roads of the Ozark Mountains, Missouri’s diverse terrain demands the mastery of air brakes for hauling heavy loads in these regions. Key transportation routes include I-70 (major east-west route from St. Louis to Kansas City), I-44 (passes through the Ozarks with steep grades), Route 60 (east-west corridor with hilly terrain), and I-55 (follows the Mississippi River). Given these challenges (and the opportunities they provide), the restriction “L” would severely limit your job prospects.
The Show Me State relies on drivers with the air brake qualification in key industries, including agriculture, manufacturing and freight (Boeing and Ford), and tourism (Branson and Lake of the Ozarks). Major companies requiring this qualification include Hogan Transportation (St. Louis), Prime Inc. (Springfield), and YRC Freight (Kansas City) in the logistics sector, as well as Jefferson Lines (Kansas City and St. Louis) and Metro Transit (St. Louis) in the charter bus and public transit industry. Missouri’s school districts also employ thousands of air brake-qualified drivers for their full-size school buses. The “L” restriction makes all these opportunities unattainable.
Our CDL Air Brakes Practice Tests cover all key information for the official DOR Air Brakes Knowledge Test. The information you learn will also be useful as you practice inspecting and operating CMVs to pass your skills test. Featuring multiple-choice questions that are based on the state’s CDL manual (Missouri CDL Handbook 2025), the written Air Brakes knowledge test requires a score of at least 80% to pass.
Our practice tests also provide real-time feedback on all responses. This scientifically proven approach helps you learn faster and ensures you pass the test.
- Perfect for first-time and renewal CDL/CLP applicants, and those adding endorsements
- Triple-checked for accuracy
What you need to know
What to expect on the actual MO DOR exam
questions
correct answers to pass
passing score
List of questions (classic view)
- How would you check your truck's slack adjusters?
- How can you tell if your vehicle is equipped with an anti-lock braking system (ABS)?
- What is the best way to test your vehicle's low air pressure warning signal?
- Which of the following will be true about your brake function if your anti-lock braking system (ABS) fails?
- How do brakes work on a long, steep downgrade?
- Which of the following should you do before leaving your vehicle unattended?
- The purpose of a supply pressure gauge is
- When should you use the parking brake?
- If the air tanks are not drained,
- Which of the following are true about a dual air brake system?
- Which vehicles must have low air pressure warning signals?
- An anti-lock braking system (ABS)
- After the initial drop, the maximum acceptable leakage rates per minute are
- Which of the following is NOT part of the air brake system?
- When should you drain your air tanks?
- The tractor protection valve
- Why must you pass a knowledge test on air brakes?
- Which of the following is NOT part of the drum brake?
- Which of the following is NOT part of the braking process when driving a tractor-trailer combination vehicle with an anti-lock braking system (ABS)?
- Which of the following can cause brakes to fade or fail?
- Under which conditions are front wheel brakes good?
- Spring brakes are
- At what measurement is the safety valve USUALLY set to open?
- Slack adjusters are
- What is the best way to test if your vehicle's spring brakes come on automatically?
- The low air pressure warning signal will come on before the pressure in the air tanks falls below
- A low pressure warning signal is required on
- All vehicles equipped with air brakes have
- With air brake-equipped vehicles, the parking brakes should be used
- The use of air brakes on a downgrade is only a supplement to the
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