25 realistic Air Brakes practice questions for Michigan CDL applicants. Required for: Vehicles equipped with air brake systems. Official test: 25 questions, 20 correct to pass.
Question 1 of 25 · Spring Brakes
Spring brakes:
-
A.
Are released by air pressure
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B.
Are applied by air pressure
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C.
Should be tested by pumping the brake pedal
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D.
Are only on the trailer
Correct answer: A.
Spring brakes are held off (released) by air pressure. When pressure drops, the springs apply the brakes.
Question 2 of 25 · Speed Management
Total stopping distance for an air-braked vehicle is made up of:
-
A.
Perception distance + reaction distance + brake lag distance + braking distance
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B.
Just the braking distance
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C.
Reaction distance only
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D.
Brake lag distance only
Correct answer: A.
It is the sum of perception distance, reaction distance, brake lag distance, and braking distance.
Question 3 of 25 · Speed Management
Brake fade results from:
-
A.
Oversized brakes
-
B.
Excessive heat from prolonged braking
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C.
Too much air pressure
-
D.
Cold weather
Correct answer: B.
Brake fade is caused by overheating brakes that lose stopping power.
Question 4 of 25 · Inspection
When should you check the parking brake?
-
A.
Whenever you start a trip
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B.
Once a month
-
C.
Only at inspections
-
D.
When the brake warning light is on
Correct answer: A.
Test the parking brake every trip — apply the brake and try to move forward gently.
Question 5 of 25 · Spring Brakes
Where are spring brakes typically NOT found?
-
A.
Front steering axle
-
B.
Drive axles
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C.
Trailer axles
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D.
Tractor rear axles
Correct answer: A.
Spring brakes are found on drive axles and trailer axles, not normally on the steering axle.
Question 6 of 25 · ABS
What is the proper procedure for an air brake stop in a vehicle equipped with ABS?
-
A.
Pump the brakes
-
B.
Press the brake pedal firmly and steadily; let ABS work
-
C.
Disengage ABS first
-
D.
Apply the parking brake
Correct answer: B.
With ABS, brake firmly and steadily. ABS prevents wheel lockup automatically.
Question 7 of 25 · System Basics
Which of these is NOT a part of the basic air brake system?
-
A.
Air compressor
-
B.
Air storage tanks
-
C.
Hydraulic master cylinder
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D.
Foot brake valve
Correct answer: C.
Hydraulic master cylinders belong to hydraulic brake systems, not air brake systems.
Question 8 of 25 · Parking
Why should you use chocks?
-
A.
When parking on a hill
-
B.
On level ground when leaving the vehicle
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C.
Whenever brakes might fail or it's required by company policy or law
-
D.
All of the above
Correct answer: D.
Chocks should be used when required to prevent vehicle movement.
Question 9 of 25 · Parking
You should never use the trailer hand valve to park because:
-
A.
It is not strong enough
-
B.
The air could leak out, releasing the brakes
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C.
It only applies the front brakes
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D.
It is not connected to the trailer
Correct answer: B.
If air leaks out, the brakes release. Always use the parking brake to park.
Question 10 of 25 · Gauges
You should know your vehicle is properly equipped with which gauge?
-
A.
Two air pressure gauges (or one with two needles) showing pressure in primary and secondary tanks
-
B.
A vacuum gauge
-
C.
A voltage meter only
-
D.
A coolant gauge only
Correct answer: A.
Dual air systems require gauges for both primary and secondary air supplies.
Question 11 of 25 · Gauges
The supply pressure gauge tells you:
-
A.
The pressure of brake fluid
-
B.
How much air pressure is in the air tanks
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C.
The trailer brake pressure
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D.
The temperature of the brake
Correct answer: B.
The supply gauge shows the air pressure available in the storage tanks.
Question 12 of 25 · Inspection
What is the air loss rate for combination vehicles with brakes applied?
-
A.
1 psi per minute
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B.
2 psi per minute
-
C.
3 psi per minute
-
D.
4 psi per minute
Correct answer: D.
Combination vehicles can lose up to 4 psi per minute with brakes applied.
Question 13 of 25 · Inspection
How can you check the slack adjusters?
-
A.
Pull hard on each slack adjuster — they should not move more than about 1 inch
-
B.
Listen for air leaks at each chamber
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C.
Watch the brake light flash
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D.
Look at the brake pedal travel
Correct answer: A.
Pulling hard, slack adjusters should not move more than about 1 inch where the push rod attaches.
Question 14 of 25 · Speed Management
Why is it important not to over-apply the brakes?
-
A.
Brakes can overheat and fade
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B.
Brakes will lock and skid
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C.
You may lose control of the vehicle
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D.
All of the above
Correct answer: D.
Over-application leads to fade, lockup, skidding, and loss of control.
Question 15 of 25 · Operation
When the brake pedal is pushed harder, what happens?
-
A.
Brake pedal must be pumped to release
-
B.
More air goes to the brakes; less foot pressure releases air
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C.
It locks the brakes permanently
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D.
The brakes do not respond
Correct answer: B.
The harder you push, the more air pressure is sent to the brake chambers.
Question 16 of 25 · Compressor
What is the purpose of a one-way check valve?
-
A.
Allow air to flow in one direction
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B.
Allow water to drain
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C.
Prevent the trailer from moving
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D.
Increase pressure in the supply tank
Correct answer: A.
It permits airflow in one direction only — protecting the system if the compressor fails.
Question 17 of 25 · Combination Air
When a tractor protection valve closes, it:
-
A.
Opens the air supply to the trailer
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B.
Stops air from going to the trailer brakes
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C.
Causes the parking brake to release
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D.
Has no effect on the trailer
Correct answer: B.
When closed, it stops airflow to the trailer and applies trailer emergency brakes.
Question 18 of 25 · Combination Air
What does the trailer hand valve do?
-
A.
Operates only the trailer brakes
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B.
Operates both the tractor and trailer brakes
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C.
Engages the parking brakes
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D.
Lowers the landing gear
Correct answer: A.
The hand valve (trolley valve) controls only the trailer service brakes.
Question 19 of 25 · Speed Management
Air brake lag distance at 55 mph on dry pavement adds about:
-
A.
12 feet to stopping distance
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B.
32 feet to stopping distance
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C.
50 feet to stopping distance
-
D.
100 feet to stopping distance
Correct answer: B.
Air brake systems have a lag of about 0.4 seconds, adding roughly 32 feet at 55 mph.
Question 20 of 25 · ABS
Which is true about ABS?
-
A.
It activates only on dry roads
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B.
It activates only when wheels are about to lock during heavy braking
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C.
It is the same as anti-skid
-
D.
It eliminates the need for skid recovery
Correct answer: B.
ABS activates only when wheels are about to lock; otherwise the brake system operates normally.
Question 21 of 25 · Foundation Brakes
Brake drums (or discs) must not have cracks longer than:
-
A.
1/4 the width of the friction area
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B.
1/2 the width of the friction area
-
C.
3/4 the width of the friction area
-
D.
Anything is acceptable
Correct answer: B.
Cracks longer than one-half the width of the friction area are a safety violation.
Question 22 of 25 · Compressor
Which of these systems removes water and oil from compressed air?
-
A.
Air dryer
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B.
Brake chamber
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C.
Slack adjuster
-
D.
S-cam
Correct answer: A.
The air dryer removes moisture and oil from the air before it reaches the storage tanks.
Question 23 of 25 · Foundation Brakes
When checking the slack adjuster on S-cam brakes, the slack adjuster should not move more than:
-
A.
1/2 inch
-
B.
1 inch
-
C.
About 1 inch where the push rod attaches to it
-
D.
2 inches
Correct answer: C.
When pulled by hand, the slack adjuster shouldn't move more than about an inch where the push rod attaches.
Question 24 of 25 · Speed Management
Which of these statements is true about brake fading?
-
A.
Resting brakes does not bring back braking power
-
B.
Brake fade is caused by drums getting too hot
-
C.
Brake fade only affects new vehicles
-
D.
Brake fade only happens with disc brakes
Correct answer: B.
Brake fade results from overheated drums or discs reducing friction and braking ability.
Question 25 of 25 · Spring Brakes
What does a "spring brake" mean?
-
A.
A brake that operates only in spring weather
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B.
A mechanical brake that uses powerful springs to apply the brake when air pressure is lost
-
C.
A specific kind of disc brake
-
D.
A backup hydraulic brake
Correct answer: B.
Spring brakes use powerful coil springs to apply the brakes when air pressure is lost.
About the Air Brakes Test
The Air Brakes test covers air brake system parts (compressor, governor, reservoirs, drain valves, alcohol evaporator, safety valve, brake pedal, foundation brakes), dual air brake systems, inspecting air brakes, using air brakes (normal stops, emergency stops, parking brakes), and proper procedures for braking on downgrades. If you fail or skip the Air Brakes test, your CDL is restricted to vehicles without full air brake systems.
The Michigan Secretary of State — Driver Services administers this knowledge test as part of its commercial driver license program. To earn the Air Brakes Endorsement on your Michigan CDL, you need to score at least 20 out of 25 on the official version.
Topics covered on this practice test
- Speed Management: 5 questions
- Spring Brakes: 3 questions
- Inspection: 3 questions
- ABS: 2 questions
- Parking: 2 questions
- Gauges: 2 questions
- Compressor: 2 questions
- Combination Air: 2 questions
- Foundation Brakes: 2 questions
- System Basics: 1 question
- Operation: 1 question
How to use this practice test
- Read each question carefully. CDL questions are written precisely — small wording differences matter.
- Click "Show Answers & Explanations" only after answering every question. Don't peek mid-test.
- Read the explanation for every question, even ones you got right. The reasoning is more important than the answer.
- Repeat the test until you score 100%. The questions are deterministic per state, so you can track your improvement over multiple sessions.
- Move on to the other endorsement tests for Michigan until you're ready for the official exam.
Tips specific to the Air Brakes test
Air Brakes questions test your ability to identify components, follow inspection sequences, and respond to system failures. Memorize the cut-in and cut-out pressures, the low-pressure warning thresholds, the pressure ranges at which spring brakes apply, and the maximum allowable air-loss rates. Many questions have nearly-identical wording, so precision matters.