CDL Air Brakes Practice Test 1

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Questions and Answers

When should you drain the air tanks if you do not have an automatic tank drain?

After every working day.

What is the S-cam used for?

To apply the brakes.

Which of the following makes the total stopping distance for air brakes longer than that for hydraulic brakes?

Hydraulic pressure

Friction coefficient

Brake pad material

Brake lag distance (correct)

What is the brake system that applies and releases the brakes when the driver uses the brake pedal?

Service brake system. Signup and view all the answers

How should you make an emergency stop with air brakes using the stab braking method?

Brake as hard as you can, get off the brakes when the wheels lock, get back on the brakes when the wheels start rolling again. Signup and view all the answers

Brake lag distance at 55 mph is _____ feet?

32 Signup and view all the answers

What is the function of an alcohol evaporator in air brake systems?

Reduce the risk of ice in air brake valves in cold weather. Signup and view all the answers

What can legally hold a parking or emergency brake in position for a truck, truck tractor or bus?

Spring pressure. Signup and view all the answers

The braking power of the spring brakes depends on:

The adjustment of the service brakes. Signup and view all the answers

Which of the following should you do before leaving your vehicle unattended?

Do all of the above. Signup and view all the answers

Under which conditions are front wheel brakes good?

All weather conditions. Signup and view all the answers

If the air tanks are not drained, what may happen?

Your brakes may fail because of water freezing. Signup and view all the answers

Which of the following can cause brakes to fade or fail?

All of the above Signup and view all the answers

What is the best way to test if your vehicle's spring brakes come on automatically?

All of the above are correct. Signup and view all the answers

If your vehicle has a properly functioning dual air brake system and minimum-sized air tanks, the air pressure should build from 85 to 100 psi within ____ seconds.

45 Signup and view all the answers

The air compressor will stop pumping air into the air tanks at ____ psi.

125 Signup and view all the answers

When does an antilock braking system (ABS) activate?

When your wheels are about to lock up. Signup and view all the answers

What excessive heat caused by overuse of the service brakes can cause?

The brakes to fade. Signup and view all the answers

What can excessive use of the service brakes lead to, which can result in overheating?

Expansion of the brake drums. Signup and view all the answers

A typical air brake system is fully charged at what pressure?

125 psi. Signup and view all the answers

During normal driving, spring brakes are usually held back by:

Air pressure. Signup and view all the answers

During your final air brake check, if the air pressure does not build up fast enough, what might happen?

The air pressure may drop too low during driving. Signup and view all the answers

To test the static air leakage rate, what should you do?

Turn off the engine, release the parking brake, and let the system settle. Signup and view all the answers

Air brakes use _________ to make the brakes work.

compressed air Signup and view all the answers

What happens when you press the brake pedal?

Compressed air enters the brake chambers. Signup and view all the answers

Study Notes

Air Brakes Overview

Oil and water can accumulate in compressed air tanks; drain these tanks after every working day if there’s no automatic drain.
Air brakes utilize compressed air to function.

Brake Components and Functions

The S-cam mechanism is crucial for applying brakes.
Service brake system engages and releases brakes when pressing the brake pedal.
Spring brakes require spring pressure to maintain position for parking or emergencies.

Stopping Distances and Methods

Brake lag distance contributes to longer stopping distances for air brakes compared to hydraulic brakes. At 55 mph, the brake lag distance is 32 feet.
To execute an emergency stop using stab braking, brake forcefully, release when wheels lock, then reapply when wheels start rolling again.

Brake Maintenance and Safety

Regular drainage of air tanks is essential to prevent brake failure due to freezing water.
Before leaving a vehicle unattended, set parking brakes, remove keys, and chock wheels.

Operating Conditions and Brake Performance

Front wheel brakes perform well under all weather conditions.
Excessive use of service brakes, improper engine braking, or brakes being out of adjustment can lead to brake fade or failure.

Testing and System Functions

To test spring brakes, repeatedly step on and off the brake pedal until specified psi is reached for engagement or the parking brake valve activates.
In a dual air brake system, pressure should build from 85 to 100 psi within 45 seconds.
The air compressor will cease pumping at 125 psi, and the system is fully charged at this pressure.

Troubleshooting and Performance Issues

The antilock braking system (ABS) functions to prevent wheel lock-up during braking.
Overuse of service brakes can cause excessive heat, leading to fade and expansion of brake drums.
During air brake checks, ensure the air pressure builds adequately to avoid drops during driving.

Air Brake Mechanics

When the brake pedal is pressed, compressed air moves into the brake chambers, facilitating braking action.
To evaluate the static air leakage rate, turn off the engine, release the parking brake, and monitor system settling.

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Description

Prepare for your CDL air brakes test with this comprehensive practice quiz. It covers essential topics like tank maintenance and braking systems, ensuring you're well-informed for your driving exam. Test your knowledge and improve your understanding of air brake functions.