Learning Hub

Welcome to your CDL Class A Permit Practice Test: Air Brakes

What does a dual air brake system allow a vehicle to do?

Operate two separate brake systems for added safety in case one fails

Switch between hydraulic and air braking automatically

Engage trailer brakes separately from tractor brakes

Use one system for service brakes and one for fuel efficiency

None

How can a driver confirm whether their vehicle is equipped with an antilock braking system (ABS)?

By looking for a warning label on the air tank

By observing the color of the brake chambers

By testing for brake lock-up during a sudden stop

By checking for a yellow ABS indicator light on the dashboard during startup

None

What is the purpose of a supply pressure gauge in a vehicle equipped with air brakes?

To release pressure from the brake chambers manually

To measure the force applied to the brake pedal

To monitor the air pressure available in the primary and secondary tanks

To control when the air compressor turns on and off

None

What is the maximum air pressure loss allowed during an APPLIED leakage test (brakes fully applied)?

Less than 3 PSI for combination vehicles in 90 seconds

Less than 5 PSI for all vehicles in 2 minutes

Less than 3 PSI for a single vehicle / less than 4 PSI for a combination vehicle in 60 seconds

Less than 2 PSI for a single vehicle / less than 3 PSI for a combination vehicle in 60 seconds

None

What is the maximum acceptable air leakage rate for a straight truck or bus during a STATIC brake test?

Less than 5 PSI for combination vehicles in 2 minutes

Less than 2 PSI for any vehicle in 30 seconds

Less than 3 PSI for a single vehicle / less than 4 PSI for a combination vehicle in 60 seconds

Less than 2 PSI for a single vehicle / less than 3 PSI for a combination vehicle in 60 seconds

None

When driving a tractor-trailer equipped with ABS, what is the proper way to apply the brakes during an emergency stop?

Brake firmly and hold the pedal down; the ABS will prevent wheel lock-up

Use only the trailer brake to prevent skidding

Apply light, steady pressure to avoid triggering the ABS

Pump the brakes quickly to engage the system manually

None

What is the function of slack adjusters in an air brake system?

To apply force to the brake pedal during emergency braking

To control the pressure level in the air tanks

To adjust the clearance between brake components and maintain proper brake function

To balance the braking force between front and rear axles

None

You do not need to set the parking brake if you are leaving the vehicle for only a short time.

False

True

None

How can a driver test whether the low air pressure warning signal is working correctly?

Press and hold the brake pedal while the engine is running—the warning light should flash after 30 seconds

Check the warning system fuse in the electrical panel during the vehicle inspection

Pull the parking brake while driving slowly and watch for the warning light

Turn off the engine, release the parking brake, and pump the brake pedal until pressure drops—the warning should activate before reaching 60 PSI

None

What is the primary function of spring brakes on vehicles with air brake systems?

To boost air pressure during heavy braking

To release air from the system during vehicle shutdown

To provide emergency and parking brake functions using spring force when air pressure is lost

To adjust brake slack automatically under load

None

If the ABS is not working, your regular braking system will still function normally.

False

True

None

What is the main reason for regularly draining air tanks in a vehicle with air brakes?

To remove excess air and maintain pressure levels

To release built-up water and oil that can damage the system

To balance the pressure between tanks

To ensure the parking brake will engage

None

What is a correct method for checking slack adjuster free play on an air brake system?

Pull hard on each slack adjuster with the brakes released; it should not move more than about 1 inch

Release the parking brake and roll the vehicle forward slowly

Step on the brake pedal and observe the slack adjuster motion

Open the air tank drain valve and listen for air release

None

All vehicles equipped with air brakes are required to have a low air pressure warning signal.

False

True

None

On long, steep downgrades, the brakes should be used only as a supplement to the engine braking effect.

False

True

None

Why is it critical to select the correct gear before descending a steep hill?

Because automatic transmissions will always shift correctly on their own

Because higher gears use less fuel when coasting downhill

Because engine braking is only needed during uphill climbs

Because shifting to a lower gear while going downhill can cause brake failure or loss of control

None

What is one way to check if the spring brakes engage automatically when air pressure gets too low?

Apply the service brakes and observe whether the air tanks refill

With the engine off and parking brake released, pump the brake pedal until the air pressure falls—watch for the parking brake to pop out

Release the parking brake, turn the wheel sharply, and press the accelerator to see if the vehicle moves

Monitor the air gauge while driving uphill with the engine off

None

How frequently should air tanks be drained to maintain safe brake system operation?

Daily, at the end of each driving day

Every time you stop for fuel

Only when the low air pressure warning comes on

Once per week, unless driving in wet conditions

None

Which of the following factors can lead to brake fade or brake failure in a vehicle with air brakes?

Applying the parking brake while driving

Excessive use of the brakes on long downhill grades

Keeping the air tanks fully drained

Using engine braking too often at low speeds

None

Front wheel brakes perform effectively and are safe to use under all driving conditions.

False

True

None

Time's up

Ready to go further? You can take this practice quiz as many times as you need — it’s here to help you feel confident and prepared for your real DMV permit test.

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