Air Brakes - Driver Resource Center

This free CDL practice test will focus on 30 questions related to the Air Brake portion of the exam. For this you will need to know the parts of a single and dual air brake system, how to inspect and use them. Be sure to also take the General Knowledge and Combination Vehicle practice tests.

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To use the stab braking technique during emergency braking, you

Pump the brake pedal rapidly and lightly

Brake hard with the pedal until the wheels lock, then get off the brakes until the wheels begin to roll again

Brake hard with the pedal until the wheels lock, then get off the brakes for as long as the wheels were locked

Brake hard with the pedal and hand valve until you stop

None

If your vehicle has an alcohol evaporator, it is there to

Get rid of alcohol that condenses in the air tanks

Let the driver skip the daily tank draining

Increase tank pressure the way superchargers boost engines

Reduce the risk of ice in the air brake valves in cold weather

None

Why should you not fan the brakes on and off during long downgrades?

Air usage is less when fanning

Brake linings do not get hot when fanning

The short time off the brakes does not allow for brake cooling

None of the above

None

Air loss in a single vehicle (not a combination unit) should not be more than ______ with the engine off and the brakes on.

1 psi in 30 seconds

1 psi in one minute

2 psi in 45 seconds

3 psi in one minute

None

Which of the following answers is most correct about using brakes on a long and/or steep downgrade?

Use the braking effects of the engine and when the vehicle speed reaches the “safe” speed, apply brakes firmly until vehicle speed is reduced to approximately 5 mph below “safe” speed

Use stab braking

Use only the trailer brakes to maintain “safe” speed

Apply brakes when the vehicle speed reaches 5 mph over “safe” speed and then release when speed of vehicle is back at the “safe” speed

None

A straight truck or bus air brake system cannot leak more than ______ psi per minute with the engine off and the brakes released.

None

How do you check the free play in manual slack adjusters?

Stop on level ground and apply the emergency brakes

Park on level ground, chock wheels, release the parking brakes and pull slack adjusters

Park on level ground and drain off air pressure before making adjustments

Apply the service brakes by hand at the brake chambers and watch the slack adjusters move

None

Air brake equipped vehicles must have

At lease three air tanks

A hydraulic braking system, in case the air system fails

An air pressure gauge, to show the pressure available for braking

An air application gauge, to show air used by the brake chambers for braking

None

The most common type of foundation brake found on heavy commercial vehicles is

Disc

Wedge and drum

S-cam drum

None of the above

None

10.

When using the parking brakes or emergency brakes, what type of pressure is being used?

Fluid pressure

Spring pressure

Air pressure

Any of the above

None

11.

Which brake system applies and releases the brakes when the driver uses the brake pedal?

The emergency brake system

The service brake system

The parking brake system

None of the above

None

12.

The brake pedal

Is the main control in the system

Can be a foot rest during normal driving

Controls the air pressure applied to operate the brakes

Exerts force on the slack adjusters by rods and connectors

None

13.

What turns on the electrical stop light switch in an air brake system?

Spring pressure

Hydraulic pressure

Air pressure

The driver, by hand

None

14.

If your truck or bus has dual parking control valves, you can use pressure from a separate tank to

Release the emergency brakes to move a short distance

Apply more brake pressure for stopping if the main tank is getting low

Stay parked without using up service air pressure

Balance the service brake system while you drive

None

15.

The air supply pressure gauge shows the driver how much pressure

Has been used in this trip

Is available in the air tanks

Is being sent to the brake chambers

None of the above

None

16.

In air brake equipped vehicles, you use the parking brakes when?

When slowing down

As little as possible

Whenever you park the vehicle

Only during pre-trip and post-trip inspections

None

17.

The air compressor governor controls

The rpms of the air compressor

Whether the compressor is in good condition

Air pressure applied to the brakes

When the compressor will pump air into the storage tanks

None

18.

Which of the following statements about brakes is true?

The heavier a vehicle or the faster it is moving, the more heat the brakes have to absorb to stop it

Brakes have more stopping power when they get very hot

Brake drums cool very quickly

All of the above are true

None

19.

You must make a quick emergency stop. You should brake so you

Can steer hard while braking hard

Use the full power of the brakes and lock them

Can stay in a straight line and maintain steering control

Burn up the hand brake first

None

20.

Three different systems are found on modern air brake systems; service brakes, parking brakes, and the

Emergency brakes

Foot brakes

S-cam brakes

Drum brakes

None

21.

Which of the following is O.K. to find in the air brake system?

Oil

Air

Water

All of the above

None

22.

If your vehicle is equipped with an alcohol evaporator, every day during the winter weather you should

Check and fill the alcohol level

Change the alcohol with a new bottle

Oil the system with 5 wt. oil

Drain out the alcohol which has accumulated

None

23.

During normal operations, the parking and emergency brakes are usually held back by

Air pressure

Spring pressure

Centrifugal force

Bolts or clamps

None

24.

The purpose of engine retarders is to

Provide emergency brakes

Help slow the vehicle while driving and reduce brake wear

Apply extra braking power to the non-drive axles

Help prevent skids and slides

None

25.

A combination vehicle air brake system cannot leak more than ______ psi per minute with the engine off and the brakes released.

None

26.

The vehicle must have a warning device which comes on when the air pressure in the service air tanks falls below

40 psi

50 psi

60 psi

80 psi

None

27.

When a failure occurs in the service brake system, the system you need to stop the vehicle is the

Parking brake system

Emergency brake system

Drum brake system

Hand brake system

None

28.

What will determine how effective the spring emergency brakes or the parking brakes work?

The condition of the service brakes

This can only be tested by highly trained brake service people

The adjustment of the service brakes

Braking power will increase when the service brakes are hot

None

29.

If the air system should develop a leak, what will keep the air in the air tanks?

The governor

The tractor protection valve

The emergency relay valve

The one-way check valve

None

30.

The air loss rate for a straight truck or bus with the engine off and the brakes applied should not be more than

1 psi in 60 seconds

1 psi in one minute

2 psi in 45 seconds

3 psi in one minute

None

Great job you’ve finished the Air Brakes CDL Practice test! Please enter your name and email. Your results will be presented on the next page. Feel free to retake the test as many times as you need to.

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This free CDL practice test will focus on 30 questions related to the Air Brake portion of the exam. For this you will need to know the parts of a single and dual air brake system, how to inspect and use them. Be sure to also take the General Knowledge and Combination Vehicle practice tests.

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