Class A · Air Brakes
Air Brakes practice test
20 free questions to answer on this page, each with its explanation and the manual section. The app has all 150, with exam mode and a mistakes list.
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Question 1 of 20 · Section 5
Which braking system applies and releases the brakes when you use the parking control?
Answer: C, The parking brake system
The parking brake system works the parking brakes from the parking brake control.
Air Brakes · Section 5 · California CDL Handbook
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Question 2 of 20 · Section 5.1
According to the manual, how is the air compressor connected to the engine?
Answer: A, Through gears or a v-belt
The engine turns the compressor, either through gears or with a v-belt, and the compressor fills the storage tanks.
Air Brakes · Section 5.1.1 · California CDL Handbook
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Question 3 of 20 · Section 5.1
How may an air compressor be cooled?
Answer: D, By air or by the engine cooling system
The compressor may be air cooled or cooled by the engine's cooling system, and it may have its own oil supply or use engine oil.
Air Brakes · Section 5.1.1 · California CDL Handbook
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Question 4 of 20 · Section 5.1
At roughly what tank pressure does the governor stop the air compressor from pumping (the cut-out level)?
Answer: C, About 125 psi
The governor stops the compressor at the cut-out level, around 125 psi, and lets it pump again when pressure falls to the cut-in level, around 100 psi.
Air Brakes · Section 5.1.2 · California CDL Handbook
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Question 5 of 20 · Section 5.1
How do you operate a manual air tank drain?
Answer: B, Turn it a quarter turn or pull a cable
Manual drains open with a quarter turn or a pull on a cable. You must drain these tanks yourself at the end of each day of driving.
Air Brakes · Section 5.1.4 · California CDL Handbook
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Question 6 of 20 · Section 5.1
Why do some automatic air tank drains have electric heaters?
Answer: D, To keep the drain from freezing in cold weather
Automatic drains push out water and oil on their own, and heating devices help keep them from freezing in cold weather.
Air Brakes · Section 5.1.4 · California CDL Handbook
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Question 7 of 20 · Section 5.1
At what pressure is the safety relief valve usually set to open?
Answer: A, 150 psi
This valve keeps the air tanks and lines from being overpressured and normally opens at 150 psi. If it lets air out, something is wrong, so have a mechanic fix it.
Air Brakes · Section 5.1.6 · California CDL Handbook
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Question 8 of 20 · Section 5.1
How does a wedge brake apply the brake shoes?
Answer: D, A push rod forces a wedge between the shoes
In a wedge brake, the brake chamber push rod drives a wedge between two brake shoes and pushes them out against the drum.
Air Brakes · Section 5.1.8 · California CDL Handbook
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Question 9 of 20 · Section 5.1
Some buses have dual parking control valves and a separate air tank. What is the separate tank for?
Answer: D, Releasing the spring brakes to move in an emergency
That tank holds enough air to release the spring brakes only a few times, so plan your moves carefully.
Air Brakes · Section 5.1.15 · California CDL Handbook
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Question 10 of 20 · Section 5.1
Does ABS always shorten your stopping distance?
Answer: A, Not necessarily, but it helps you keep control
ABS may or may not shorten your stop. What it does is help you keep the vehicle under control during hard braking.
Air Brakes · Section 5.1.16 · California CDL Handbook
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Question 11 of 20 · Section 5.2
Before driving a vehicle with a dual air brake system, the compressor should build pressure to at least how much in both the primary and secondary systems?
Answer: A, 100 psi
Give the compressor time to build at least 100 psi in both systems before you drive. Watch both gauges, or both needles if there is one gauge.
Air Brakes · Section 5.2 · California CDL Handbook
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Question 12 of 20 · Section 5.3
Before troubleshooting an automatic slack adjuster, what should you check?
Answer: B, The maker's service manual
Automatic slack adjusters from different manufacturers do not all work the same way, so consult the specific maker's service manual first.
Air Brakes · Section 5.3.2 · California CDL Handbook
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Question 13 of 20 · Section 5.3
During the walk-around, on which kind of brakes do you check the slack adjusters?
Answer: A, S-cam brakes
Check the slack adjusters on S-cam brakes by pulling hard on each one you can reach, with the parking brakes released.
Air Brakes · Section 5.3.2 · California CDL Handbook
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Question 14 of 20 · Section 5.3
During the walk-around, what should be true of the brakes' mechanical parts?
Answer: A, They are in place, not broken or missing
Check that the brakes' mechanical parts are in place and not broken or missing, along with the drums, linings, and hoses.
Air Brakes · Section 5.3.2 · California CDL Handbook
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Question 15 of 20 · Section 5.3
How do you lower the air pressure during the low air warning test?
Answer: A, Apply and release the foot brake over and over
With enough pressure that the warning is off, fan the air down by pressing and releasing the foot brake until the warning comes on.
Air Brakes · Section 5.3.3.2 · California CDL Handbook
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Question 16 of 20 · Section 5.4
During a normal stop in a vehicle with a manual transmission, when should you push in the clutch?
Answer: C, When engine rpm is down close to idle
Brake smoothly and keep the clutch out until the engine has slowed to near idle. Once stopped, pick a starting gear.
Air Brakes · Section 5.4.1 · California CDL Handbook
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Question 17 of 20 · Section 5.4
Without ABS, what happens when your steering wheels lock up during hard braking?
Answer: B, You lose steering control
Locked steering wheels cannot steer the vehicle. Locked rear wheels can make it skid, jackknife, or spin.
Air Brakes · Section 5.4.2 · California CDL Handbook
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Question 18 of 20 · Section 5.4
Your tractor has ABS but the trailer does not. What does the tractor's ABS help with?
Answer: C, Keeping steering control, with less chance of a jackknife
With ABS on the tractor only, you should keep steering control and are less likely to jackknife, but still watch the trailer.
Air Brakes · Section 5.4.2 · California CDL Handbook
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Question 19 of 20 · Section 5.4
Brake fade comes from excessive heat. What does that heat do to the brakes?
Answer: D, The linings grip less and the drums expand
Heat causes chemical changes in the lining that cut friction, and the drums expand, so the shoes must travel farther and press less firmly.
Air Brakes · Section 5.4.5 · California CDL Handbook
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Question 20 of 20 · Section 5.4
Your vehicle has no automatic tank drains. When should you drain the air tanks?
Answer: B, At the end of each working day
Draining daily removes moisture and oil. If you skip it, the brakes could fail.
Air Brakes · Section 5.4.8 · California CDL Handbook
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The full bank is in the app
All 150 Air Brakes questions, an exam mode with 25 questions and the 80% pass mark, explanations for every answer, and a mistakes list that keeps what you missed until you clear it.
Coming soon to the App Store and Google Play.
What the Air Brakes test covers
Section 5 of the CDL manual. You take this test if your vehicle has air brakes, including air over hydraulic brakes (Section 1.1.1). Skip it or fail it, and your license carries restriction L: no vehicles with air brakes (Section 1, Restrictions). The section numbers are the same in the California, Texas and Florida handbooks.