Starting a job in commercial driving means learning many things, including how air brakes work. New drivers need to pass an air brake test to show they can drive safely with air brakes. This guide is here to help you prepare for your CDL air brake test so you know all you need to stay safe on the roads.
What is an air brake test?
The air brake test is crucial for operating large trucks and buses. It evaluates truck drivers' understanding and proficiency in using air brake systems, which are distinct from standard brakes. Air brakes use compressed air to stop the vehicle, and drivers should know the operations for safe driving. During the test, candidates need to demonstrate their ability to apply air brakes and respond to emergencies effectively and correctly.
The importance of air brake knowledge
Understanding how these brakes work is crucial for truck drivers as it ensures safe driving practices and helps prevent potential accidents. Proficiency in air brake operation enables drivers to control their vehicles effectively, especially in challenging situations such as emergencies or navigating steep terrain. Familiarity with air brake systems also facilitates the timely detection of any malfunctions or issues during pre-trip inspections, thereby preventing potential accidents and breakdowns. Moreover, air brake knowledge is a legal requirement for obtaining a CDL. Regulatory bodies mandate that drivers demonstrate competence in operating vehicles equipped with air brakes to uphold safety standards and comply with regulations governing commercial driving.
Overview of the CDL air brake test
The CDL air brake test checks if you know how to use air brakes on big vehicles. To take the test, you must be 18 years old, have a valid driver’s license, pass a medical exam, and know basic air brake stuff.
There are two parts: a written test and a practical one.
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Written exam: This part of the test asks questions about air brake parts, how they work, and safety rules.
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Practical exam: This part shows if you can use air brakes safely. You'll have to do tasks like checking them before driving.
Preparing for an air brake test
Preparing effectively for the CDL air brake test is the first step in passing your exam. Here are some quick tips on how you can get started with your preparation for the exam.
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Get familiar with the components: Start by understanding the different parts of air brakes and what they do. This is important for knowing how the whole system works.
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Get practical: If you can, get some practice with air brakes. You could do this through special training or by practicing with someone who knows about them.
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Practice tests: Take advantage of practice tests for air brakes. These help you see if you're ready for the real test and get used to the questions ( we have one at the end of this guide).
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Practice pre-trip inspection: Make sure you practice doing pre-trip inspections. This is really important for the test and for using air brakes safely every day.
Exam details and requirements
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Exam Features |
Details |
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Number of questions |
25 multiple-choice questions |
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Passing score |
Approximately 80%, varies by state |
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Time limit |
Around 1-2 hours, varies by state |
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Key topics |
Air brake system components, function, maintenance, inspection, proper usage, troubleshooting |
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Test format |
Computer-based in most states; practical component includes hands-on tasks |
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Retake policy |
Varies by state; waiting period and test costs or fee may apply for retakes |
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Prerequisites |
Valid CDL, 18 years of age, good medical history (requirements vary per state) |
Understanding the air brake system components
Knowing the parts of the air brake system is crucial for passing the CDL Air Brake Test. These parts include the air compressor, air tanks, brake pedal, brake chambers, slack adjusters, and brake drums or discs. Each part helps the air brake system work well and keeps the vehicle safe. Knowing about these parts and what they do is important for answering test questions correctly and doing practical tasks during the test. Here’s a quick overview of what these are:
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Air compressor: The air compressor pumps and sends air to the air tanks. It gets power from the engine and is important for keeping the air brake system working.
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Air tanks: Air tanks store compressed air from the compressor. They act like reservoirs, making sure there's always enough air for the brakes to work, even when the engine isn't running.
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Brake pedal: The driver presses the brake pedal to activate the brakes. When pressed, air is released from the tanks to push the brakes and make them work.
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Brake chambers: Brake chambers change air pressure into force to push the brakes. They have a part that moves when air is pushed in, making the brakes work.
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Slack adjusters: Slack adjusters are used to change the space between the brakes and the brake drums or discs. They make sure the brakes are working well and have the right space to move.
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Brake drums or discs: These are the parts where the brake pads touch to stop the vehicle. They work by creating friction to slow down or stop the vehicle.
Passing the test on the first try
To pass the air brake test the first time, you need to prepare well and understand air brake systems clearly. Start by learning about the air brake system parts and how they work. Focus on important ideas like air pressure, braking, and maintenance. Use practice tests to see how much you know and where you need to improve. Also, practice doing pre-trip inspections so you're ready for the practical part of the test. Stay calm and pay attention during the test, read each question carefully, and follow the instructions. With good preparation and confidence, you can increase your chances of passing the test on your first attempt.
Retaking the test after failing
If you don't pass the air brake test, don't give up. Learn from your mistakes and keep trying. Figure out what you didn't understand and how you can do better next time. You might need more study guides or extra help to understand air brake systems better. Practice regularly and use practice tests to see how much you've improved. When you feel ready, schedule another test and go in with a positive attitude. Learn from what went wrong before and stay focused on passing the CDL Air Brake Test and getting your air brake endorsement.
30 practice questions for the air brake test
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What is the first thing you should do when you make a quick stop?
a) Check your mirrors
b) Look ahead for traffic
c) Step on the brake pedal
d) Check the gauges
Answer: b) Look ahead for traffic
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What is the most important thing to do during a trip?
a) Check the traffic behind you
b) Plan your route
c) Adjust your mirrors
d) Plan for rest stops
Answer: b) Plan your route
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What is a supply pressure gauge used for?
a) To show how much air pressure you are using
b) To show how much air pressure is in the air tanks
c) To show how much air pressure is in the service line
d) To show how much air pressure is in the trailer air tank
Answer: b) To show how much air pressure is in the air tanks
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The air compressor governor controls air pressure by:
a) Turning on and off the engine
b) Pumping air into the air tanks
c) Controlling the air compressor
d) Regulating the flow of air into the air tanks
Answer: d) Regulating the flow of air into the air tanks
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What should you do if your vehicle starts to skid?
a) Turn the steering wheel in the direction of the skid
b) Step on the brake pedal as hard as you can
c) Turn the steering wheel away from the skid
d) Let up on the brake pedal
Answer: a) Turn the steering wheel in the direction of the skid
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Which of the following is NOT a part of the air brake system?
a) Brake pedal
b) Brake chambers
c) Slack adjusters
d) Exhaust brake
Answer: d) Exhaust brake
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The brake pedal in an air brake system:
a) Is always firm and hard to push
b) Should be pumped if the brakes are fading
c) Should be pushed down slowly
d) Is connected to the parking brake system
Answer: c) Should be pushed down slowly
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Which of the following is NOT part of the air brake system?
a) Air tank drains
b) Brake drums
c) Springs
d) Slack adjusters
Answer: c) Springs
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If the low-pressure warning signal comes on while driving, what should you do?
a) Stop and turn off the engine as soon as you can
b) Speed up and find the nearest service station
c) Stop and refill the air tanks
d) Continue driving and ignore the warning
Answer: a) Stop and turn off the engine as soon as you can
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What is the most important thing to do if the service line breaks?
a) Apply the parking brake immediately
b) Sound your horn to warn other drivers
c) Stop as soon as safely possible
d) Open the hood and check for damage
Answer: c) Stop as soon as safely possible
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What is a tractor protection valve?
a) A device that prevents the trailer from overturning
b) A valve that keeps air in the tractor or truck brake system should the trailer break away or develop a bad leak
c) A valve that allows the tractor protection control to be manually activated
d) A device that prevents the truck from skidding
Answer: b) A valve that keeps air in the tractor or truck brake system should the trailer break away or develop a bad leak
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All vehicles with air brakes must have:
a) A warning device
b) Anti-lock brakes
c) A backup braking system
d) A dual-air brake system
Answer: d) A dual air brake system
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The total stopping distance for air brakes is made up of ____ distance and ____ distance.
a) Pedal, reaction
b) Brake lag, tire tread
c) Perception, reaction
d) Highway, reaction
Answer: c) Perception, reaction
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What are spring brakes?
a) Air brakes that can be used as emergency brakes
b) Brakes that only work when air pressure is low
c) Brakes held off by air pressure, which are used for parking or emergencies
d) Brakes that use hydraulic pressure to stop the vehicle
Answer: c) Brakes held off by air pressure, which are used for parking or emergencies
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What should you do if your vehicle pulls toward the right when you are braking?
a) Have the brakes adjusted
b) Release the brakes and reapply them
c) Apply the brakes harder
d) Stop and check the brakes
Answer: b) Release the brakes and reapply them
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What is a dual air brake system?
a) A braking system with two separate air brake systems
b) A braking system with two separate brake pedals
c) A braking system with two separate parking brakes
d) A braking system with two separate air tanks
Answer: a) A braking system with two separate air brake systems
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What is a "bobtail" tractor?
a) A tractor without a trailer
b) A tractor with two trailers
c) A tractor with a malfunctioning air brake system
d) A tractor with a fully loaded trailer
Answer: a) A tractor without a trailer
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When driving a vehicle with a dual air brake system, the parking brakes should be used:
a) Whenever the vehicle is parked
b) Whenever the vehicle is being serviced
c) Only on steep grades
d) Only on the rear wheels
Answer: a) Whenever the vehicle is parked
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What is the proper way to test the low-pressure warning signal?
a) Charge the system to 150 psi
b) Pump the brake pedal three times
c) Shut the engine off when the air pressure gauge shows over 100 psi
d) Build the air pressure to the governor cutoff and push the brake pedal hard
Answer: c) Shut the engine off when the air pressure gauge shows over 100 psi
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When making an emergency stop with air brakes, you should:
a) Brake normally
b) Apply the parking brake
c) Use controlled or stab braking
d) Pump the brakes
Answer: c) Use controlled or stab braking
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What is the most common type of foundation brake found on heavy vehicles?
a) Air brake
b) Hydraulic brake
c) Electric brake
d) Mechanical brake
Answer: b) Hydraulic brake
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What is the purpose of an air tank drain valve?
a) To release air pressure from the system
b) To release oil from the air compressor
c) To drain moisture and oil from the air tanks
d) To increase air pressure in the system
Answer: c) To drain moisture and oil from the air tanks
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What is the brake lag distance?
a) The distance your vehicle will travel after you hit the brakes
b) The distance your vehicle will travel after you release the brakes
c) The distance your vehicle will travel after you let off the accelerator
d) The distance your vehicle will travel after you shift gears
Answer: b) The distance your vehicle will travel after you release the brakes
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What should you do if the air pressure gauge shows the air pressure dropping?
a) Check for air pressure leaks
b) Keep driving until the pressure drops to zero
c) Continue driving and ignore the gauge
d) Increase speed to build air pressure
Answer: a) Check for air pressure leaks
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What should you do if the low air pressure warning light comes on while you are driving?
a) Speed up to reach your destination faster
b) Stop and test the warning signal
c) Continue driving and ignore the warning light
d) Reduce speed and safely stop the vehicle
Answer: d) Reduce speed and safely stop the vehicle
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How often should the air compressor build air pressure from 85 to 100 psi?
a) Within 2 minutes
b) Within 3 minutes
c) Within 4 minutes
d) Within 5 minutes
Answer: a) Within 2 minutes
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What is the first thing to do when you make a turn that requires a lane change?
a) Activate your turn signal
b) Check for traffic
c) Change lanes slowly
d) Honk your horn
Answer: b) Check for traffic
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How do you know if your vehicle has ABS?
a) The ABS light on the dashboard will turn on
b) The ABS will make a loud noise
c) The ABS will automatically engage
d) The ABS will prevent the vehicle from skidding
Answer: a) The ABS light on the dashboard will turn on
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Why should you drain the air tanks?
a) To keep the air pressure low
b) To prevent oil from getting into the brake system
c) To remove moisture and oil
d) To reduce the weight of the vehicle
Answer: c) To remove moisture and oil
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What should you do if your vehicle has a dual air brake system and one air system is low on pressure?
a) Keep driving and ignore the low pressure warning
b) Drive to the nearest repair shop
c) Pump the brakes to build pressure
d) Safely stop and have the problem fixed
Answer: d) Safely stop and have the problem fixed
Pass your CDL air brake test with confidence
Acing an air brake test requires an understanding of air brake systems, thorough preparation, and practical experience. Remember to study the key components of air brake systems, practice with our free practice tests, and familiarize yourself with the test requirements. By following the tips in this guide and dedicating time to preparation, you can confidently pass your CDL air brake test. So, take the time to prepare, stay focused, and trust in your abilities. With determination and perseverance, you can conquer the CDL air brake test and take the next step toward achieving your career goals. Good luck!