Florida Air Brakes CDL Practice Test
25 realistic Air Brakes practice questions for Florida CDL applicants. Required for: Vehicles equipped with air brake systems. Official test: 25 questions, 20 correct to pass.
Question 1 of 25 · Tanks
Why must air tanks be drained?
-
A.
To remove fuel from the system
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B.
To remove water and compressor oil that can damage the brakes
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C.
To inspect the tanks
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D.
To increase pressure
Correct answer: B.
Water and oil collect in tanks. They damage seals and can freeze in cold weather.
Question 2 of 25 · Foundation Brakes
What's the most common type of foundation brake found on heavy vehicles?
-
A.
Disc brakes
-
B.
Wedge drum brakes
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C.
S-cam drum brakes
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D.
Air-over-hydraulic
Correct answer: C.
S-cam drum brakes are the most common foundation brakes on heavy commercial vehicles.
Question 3 of 25 · Compressor
The air compressor governor controls:
-
A.
When the air compressor will pump air into the storage tanks
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B.
When the brakes are applied
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C.
When emergency brakes engage
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D.
How fast the air compressor turns
Correct answer: A.
The governor cuts the compressor in and out to keep the system within its operating pressure range.
Question 4 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 5 of 25 · Bobtail
What is bobtail braking?
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A.
Braking with no trailer attached, when the tractor brakes harder than usual
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B.
A type of trailer-only braking
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C.
Emergency braking on doubles
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D.
A way to test the parking brake
Correct answer: A.
A bobtail tractor (without a trailer) brakes hard because it has less weight on the drive axles.
Question 6 of 25 · Warning Devices
The low air pressure warning device must come on when air pressure in the service tanks falls below:
-
A.
80 psi
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B.
60 psi
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C.
50 psi or 1/2 the compressor governor cut-out pressure
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D.
20 psi
Correct answer: C.
Low pressure warnings activate at 60 psi or less (or half the cut-out pressure on older vehicles).
Question 7 of 25 · Tanks
What is the safety valve set to open at?
-
A.
100 psi
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B.
125 psi
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C.
150 psi
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D.
180 psi
Correct answer: C.
The safety valve is normally set to open at 150 psi to protect the system from over-pressurization.
Question 8 of 25 · Parking
When parking a tractor-trailer with spring brakes:
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A.
Use the trailer hand valve only
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B.
Use the parking brake only — do not push the brake pedal down to hold the vehicle
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C.
Press the foot brake and then engage the parking brake
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D.
Set both brakes simultaneously
Correct answer: B.
Don't push the pedal down because it will cause damage. Set the parking brakes only.
Question 9 of 25 · ABS
What is the proper procedure for an air brake stop in a vehicle equipped with ABS?
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A.
Pump the brakes
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B.
Press the brake pedal firmly and steadily; let ABS work
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C.
Disengage ABS first
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D.
Apply the parking brake
Correct answer: B.
With ABS, brake firmly and steadily. ABS prevents wheel lockup automatically.
Question 10 of 25 · Spring Brakes
Spring brakes will come on automatically when air pressure drops to:
-
A.
100 psi
-
B.
60 psi or less
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C.
20 to 45 psi
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D.
10 psi
Correct answer: C.
Spring brakes typically apply automatically between 20 and 45 psi.
Question 11 of 25 · System Basics
Which of the following is NOT in the air brake system?
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A.
Brake chambers
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B.
Slack adjusters
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C.
S-cam
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D.
Hydraulic master cylinder
Correct answer: D.
Hydraulic master cylinders are part of hydraulic systems, not air brake systems.
Question 12 of 25 · ABS
Which is true about ABS?
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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
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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 13 of 25 · Inspection
How do you test the low pressure warning signal?
-
A.
With the engine off, pump the brake pedal until the signal activates (must come on at 60 psi or above)
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B.
Drive the vehicle to lose pressure
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C.
Open the air tank drain valve briefly
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D.
Push the parking brake control
Correct answer: A.
Pump the brake to lower pressure; warning must come on at 60 psi or higher.
Question 14 of 25 · Tanks
Air brake equipped vehicles must have:
-
A.
Only an emergency brake
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B.
A drain valve in each air tank
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C.
Hydraulic backup
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D.
Disc brakes only
Correct answer: B.
Each air tank has a drain valve to remove water and oil that collect in the tank.
Question 15 of 25 · Parking
Why should you use chocks?
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A.
When parking on a hill
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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 16 of 25 · Gauges
The supply pressure gauge tells you:
-
A.
The pressure of brake fluid
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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 17 of 25 · Spring Brakes
If your vehicle has dual parking control valves, you can use pressure from a separate tank to:
-
A.
Charge the trailer brakes
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B.
Release the spring brakes to move a short distance if the main system loses air
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C.
Operate the steering
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D.
Power the air horn
Correct answer: B.
Dual parking control valves let you temporarily release spring brakes from a backup tank.
Question 18 of 25 · Emergency Maneuvers
Which of these statements is true about emergency braking?
-
A.
Pumping the brakes is always best
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B.
Stab braking is for non-ABS vehicles in emergencies
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C.
You should brake harder than necessary
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D.
Stab braking is the same as pumping
Correct answer: B.
Stab braking applies to non-ABS systems: full application until lockup, then release.
Question 19 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 20 of 25 · Speed Management
Air brake lag is:
-
A.
The time required for the brakes to apply after the pedal is pressed
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B.
The amount of free play in the brake pedal
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C.
The distance traveled before the brakes release
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D.
The time to drain air tanks
Correct answer: A.
Lag is the time between pressing the pedal and the brakes actually applying — about 0.4 seconds.
Question 21 of 25 · Inspection
When should you check the parking brake?
-
A.
Whenever you start a trip
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B.
Once a month
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C.
Only at inspections
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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 22 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 23 of 25 · System Basics
Air brake systems combine three different braking systems. They are:
-
A.
Service, parking, and emergency brakes
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B.
Hydraulic, parking, and emergency brakes
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C.
Front, rear, and trailer brakes
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D.
Disc, drum, and parking brakes
Correct answer: A.
The three are: the service brake, the parking brake, and the emergency brake.
Question 24 of 25 · Operation
When making a normal stop, what should you do?
-
A.
Push the brake pedal down so you can stop at a safe place and remain in control
-
B.
Pump the brakes
-
C.
Use only the parking brake
-
D.
Use only the trailer hand valve
Correct answer: A.
Apply pressure progressively to come to a smooth, safe stop while maintaining control.
Question 25 of 25 · System Basics
Which of these is NOT a part of the basic air brake system?
-
A.
Air compressor
-
B.
Air storage tanks
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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.
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 Florida Department of Highway Safety and Motor Vehicles administers this knowledge test as part of its commercial driver license program. To earn the Air Brakes Endorsement on your Florida CDL, you need to score at least 20 out of 25 on the official version.
Topics covered on this practice test
- Tanks: 3 questions
- Parking: 3 questions
- System Basics: 3 questions
- Speed Management: 2 questions
- ABS: 2 questions
- Spring Brakes: 2 questions
- Inspection: 2 questions
- Foundation Brakes: 1 question
- Compressor: 1 question
- Bobtail: 1 question
- Warning Devices: 1 question
- Gauges: 1 question
- Emergency Maneuvers: 1 question
- Combination Air: 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 Florida 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.
Other practice tests for Florida