# Trivia Quiz: CDL Air Brake Practice Test

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| By Devin Hutchings
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Devin Hutchings
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Quizzes Created: 4 | Total Attempts: 58,584
Questions: 30 | Attempts: 8,506

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Questions and Answers
• 1.

### The air brake lag distance at 55 mph on dry pavement adds about ______ feet to your stopping distance?

• A.

12

• B.

52

• C.

32

Correct Answer
C. 32
Explanation
The air brake lag distance at 55 mph on dry pavement adds about 32 feet to your stopping distance. This means that when you apply the air brakes at this speed, it takes an additional 32 feet for the vehicle to come to a complete stop. This lag distance is important to consider in order to ensure safe braking and avoid collisions or accidents.

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• 2.

### The most important thing to do when a low air pressure warning comes on is?

• A.

Upshift and drive to a safe place.

• B.

Downshift and drive to a safe place.

• C.

Stop and safely park as soon as possible.

Correct Answer
C. Stop and safely park as soon as possible.
Explanation
When a low air pressure warning comes on, it is crucial to stop and safely park as soon as possible. This warning indicates that there is a problem with the air pressure in the tires, which can lead to a loss of control and potentially cause an accident. Continuing to drive with low air pressure can further damage the tires and potentially result in a blowout. Therefore, it is important to stop and address the issue by checking the tires and either inflating them or seeking professional assistance.

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• 3.

### How should you check that your service brakes are working properly?

• A.

Park on a slight incline, drain off air pressure, set the parking brakes, and check for movement.

• B.

Wait for normal pressure, release the parking brake, move the truck forward slowly, and firmly step on the brake.

• C.

Park on level ground, chock the wheels, engage the parking brake, and shut the engine off.

Correct Answer
B. Wait for normal pressure, release the parking brake, move the truck forward slowly, and firmly step on the brake.
Explanation
The correct answer suggests that in order to check if the service brakes are working properly, one should wait for normal pressure, release the parking brake, move the truck forward slowly, and firmly step on the brake. This sequence of actions allows for a comprehensive assessment of the functionality of the service brakes. By waiting for normal pressure, it ensures that the brakes are properly pressurized. Releasing the parking brake allows for the brakes to engage without interference. Moving the truck forward slowly and firmly stepping on the brake tests the responsiveness and effectiveness of the service brakes.

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• 4.

### The stop light switch:

• A.

Turns on the brake lights to warn drivers behind you.

• B.

Tells you when you need to use your emergency brakes.

• C.

Tells you when the air brake system is low on pressure.

Correct Answer
A. Turns on the brake lights to warn drivers behind you.
Explanation
The stop light switch is responsible for turning on the brake lights, which are used to warn drivers behind you that you are slowing down or stopping. This is an important safety feature that helps prevent rear-end collisions by alerting other drivers of your intentions on the road.

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• 5.

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

• A.

Rid the wet tank of alcohol that condenses and sits at the bottom.

• B.

Eliminates the need for daily tank draining.

• C.

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

Correct Answer
C. Reduce the risk of ice in air brake valves in cold weather.
Explanation
The alcohol evaporator in a vehicle is designed to reduce the risk of ice in air brake valves during cold weather. When the temperature drops, moisture in the air can condense and freeze, leading to ice formation in the air brake valves. The alcohol evaporator helps prevent this by evaporating alcohol into the air system, which lowers the freezing point of any moisture present. This reduces the likelihood of ice formation and helps ensure the proper functioning of the air brake system in cold weather conditions.

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• 6.

### The most common type of foundation brake found on heavy vehicles is the:

• A.

Wedge drum.

• B.

S-Cam drum.

• C.

Disc brake.

Correct Answer
B. S-Cam drum.
Explanation
The S-Cam drum is the most common type of foundation brake found on heavy vehicles. This type of brake system uses a rotating S-shaped cam to push the brake shoes against the inside of the drum, creating friction and stopping the vehicle. S-Cam drum brakes are preferred for heavy vehicles due to their durability, reliability, and ability to handle high braking forces. They are also cost-effective and require less maintenance compared to other types of foundation brakes.

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• 7.

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

• A.

Bolts.

• B.

Spring pressure.

• C.

Air pressure.

Correct Answer
C. Air pressure.
Explanation
Spring brakes are a type of braking system used in heavy vehicles, such as trucks and buses. These brakes are designed to engage automatically when there is a loss of air pressure in the system, such as during a leak or when the vehicle is parked. This ensures that the vehicle remains stationary and prevents it from rolling away. Therefore, the correct answer is air pressure, as it is the force that keeps the spring brakes held back during normal driving.

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• 8.

### A truck with air brakes going 55 mph would require a stopping distance of?

• A.

Less than 100 feet.

• B.

100-300 feet.

• C.

More than 300 feet.

Correct Answer
C. More than 300 feet.
Explanation
A truck with air brakes going 55 mph would require a stopping distance of more than 300 feet because larger vehicles like trucks have more momentum and require more time and distance to come to a complete stop compared to smaller vehicles. Additionally, air brakes take longer to engage and slow down the vehicle compared to hydraulic brakes, further increasing the stopping distance.

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• 9.

### Your truck has a properly functioning dual air brake system and minimum size air tanks. The air pressure should build from 85 to 100 psi within:

• A.

30 seconds.

• B.

45 seconds.

• C.

60 seconds.

Correct Answer
B. 45 seconds.
Explanation
The correct answer is 45 seconds because it is a reasonable amount of time for the air pressure to build from 85 to 100 psi in a properly functioning dual air brake system with minimum size air tanks. It allows for a gradual increase in pressure without being too fast or too slow.

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• 10.

### If your truck has a dual air system and one of the systems is low on pressure:

• A.

The brake drums will not be fully pressurized.

• B.

Either the front or rear brakes will not be fully operational.

• C.

The manual slack adjusters on the S-cam brakes are not set properly.

Correct Answer
B. Either the front or rear brakes will not be fully operational.
Explanation
If a truck with a dual air system has one of the systems low on pressure, it means that the air pressure is not sufficient to fully engage the brakes. This would result in either the front or rear brakes not being fully operational, as they rely on the proper air pressure to function effectively.

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• 11.

### In air brake vehicles, the parking brakes should be used:

• A.

As little as possible.

• B.

To hold your speed when going downhill.

• C.

Any time the vehicle is parked.

Correct Answer
C. Any time the vehicle is parked.
Explanation
The correct answer is "Any time the vehicle is parked." This means that the parking brakes should be used whenever the vehicle is not in motion and is parked. This is important for ensuring the safety and stability of the vehicle while it is stationary. By engaging the parking brakes, it helps to prevent the vehicle from rolling or moving unintentionally, especially on inclines or uneven surfaces. Therefore, it is necessary to use the parking brakes every time the vehicle is parked to maintain control and prevent accidents.

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• 12.

### The braking power of the spring brakes:

• A.

Is not affected by the condition of the service brakes.

• B.

Depends on the service brake being in adjustment.

• C.

Increases when the service brakes are hot.

Correct Answer
B. Depends on the service brake being in adjustment.
Explanation
The correct answer is "Depends on the service brake being in adjustment." The braking power of the spring brakes relies on the proper adjustment of the service brakes. If the service brakes are not properly adjusted, it can affect the braking power of the spring brakes. Therefore, the spring brakes' effectiveness is directly dependent on the adjustment of the service brakes.

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• 13.

### What is emergency stab braking?

• A.

Press hard on the brake pedal and apply full hand valve until you stop.

• B.

Use light, steady pressure on the brake pedal.

• C.

Brake hard, release the brakes when the wheels lock, and reapply the brakes when the wheels start rolling.

Correct Answer
C. Brake hard, release the brakes when the wheels lock, and reapply the brakes when the wheels start rolling.
Explanation
Emergency stab braking refers to a technique where the driver applies maximum pressure on the brake pedal, causing the wheels to lock up momentarily. This helps to quickly reduce the vehicle's speed in emergency situations. However, it is important to release the brakes when the wheels lock, allowing them to start rolling again, and then reapply the brakes to maintain control and prevent skidding. This technique allows the driver to effectively stop the vehicle in a shorter distance while still maintaining control.

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• 14.

### When you apply the brakes, the brake shoes/linings are pressed against the:

• A.

Brake drum or disc.

• B.

Slack adjuster.

• C.

S-cam.

Correct Answer
A. Brake drum or disc.
Explanation
When you apply the brakes, the brake shoes/linings are pressed against the brake drum or disc. This creates friction, which helps to slow down or stop the vehicle. The brake drum or disc is a crucial component of the braking system, as it provides a surface for the brake shoes/linings to make contact with. The friction generated between the brake shoes/linings and the brake drum or disc is what ultimately causes the vehicle to decelerate.

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• 15.

### The air compressor governor controls:

• A.

When air is pumped into the air tanks.

• B.

The speed of the air compressor.

• C.

Air pressure applied to the brakes.

Correct Answer
A. When air is pumped into the air tanks.
Explanation
The air compressor governor controls the process of pumping air into the air tanks. It regulates the amount of air being pumped and ensures that the tanks are filled to the appropriate pressure. By controlling this process, the governor helps maintain the proper air pressure in the tanks, which is crucial for the efficient operation of the vehicle's braking system.

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• 16.

### What is emergency controlled braking?

• A.

You apply the brakes as hard as you can without locking the wheels.

• B.

You brake as hard as you can, release the brakes when the wheels lock, and reapply the brakes when the wheels start rolling.

• C.

You apply the hand valve for one second, then push hard on the brake pedal.

Correct Answer
A. You apply the brakes as hard as you can without locking the wheels.
Explanation
Emergency controlled braking refers to the action of applying the brakes with maximum force without causing the wheels to lock. This technique allows the driver to effectively slow down or stop the vehicle in emergency situations while maintaining control and avoiding skidding. By applying the brakes firmly but not causing the wheels to lock, the driver can ensure that the tires maintain traction with the road surface, allowing for better steering and maneuverability.

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• 17.

### The driver must be able to see a low air pressure warning which comes on before pressure in teh service air tanks fall below ______ psi?

• A.

40

• B.

60

• C.

80

Correct Answer
B. 60
Explanation
The driver must be able to see a low air pressure warning which comes on before pressure in the service air tanks fall below 60 psi. This is important because if the pressure falls below this level, it could indicate a potential problem with the brakes or other components of the air system. By having a warning at 60 psi, the driver can take necessary precautions and address the issue before it becomes a safety concern.

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• 18.

### The safety valve is usually set to reduce air pressure at _____ psi.

• A.

50

• B.

100

• C.

150

Correct Answer
C. 150
Explanation
The safety valve is set to reduce air pressure at 150 psi. This means that when the air pressure exceeds 150 psi, the safety valve will open, releasing some of the air and reducing the pressure to a safer level. This is important in order to prevent damage to the equipment or system that the valve is protecting, as well as to ensure the safety of the individuals working with or around the equipment.

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• 19.

### Repeatedly pressing and releasing (fanning) the brake pedal may result in:

• A.

A loss of brake air pressure.

• B.

A build up of brake air pressure.

• C.

No change in brake air pressure.

Correct Answer
A. A loss of brake air pressure.
Explanation
Repeatedly pressing and releasing the brake pedal can result in a loss of brake air pressure. This is because each time the pedal is pressed, the air pressure in the brake system is released to apply the brakes. Repeatedly doing this can cause the air pressure to decrease over time, leading to a loss of brake effectiveness.

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• 20.

### The brake pedal in an air brake system:

• A.

Controls the speed of the air compressor.

• B.

Controls the air pressure applied to put on the brakes.

• C.

Is connected to slack adjusters by a series of rods and linkages.

Correct Answer
B. Controls the air pressure applied to put on the brakes.
Explanation
The brake pedal in an air brake system controls the air pressure applied to put on the brakes. This means that when the driver presses the brake pedal, it activates the air pressure system, which then applies the necessary pressure to engage the brakes and slow down or stop the vehicle. The brake pedal is not responsible for controlling the speed of the air compressor or being connected to slack adjusters by rods and linkages.

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• 21.

### If you must make an emergency stop, brake so you:

• A.

Can steer hard while braking hard.

• B.

Use the hand brake first.

• C.

Can steer your vehicle in a straight line.

Correct Answer
C. Can steer your vehicle in a straight line.
Explanation
When making an emergency stop, it is important to brake in a way that allows you to maintain control of your vehicle. By braking in a way that allows you to steer your vehicle in a straight line, you can avoid swerving or losing control of the vehicle. This is crucial in emergency situations where you need to quickly come to a stop without causing further accidents or endangering yourself and others on the road.

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• 22.

### Truck and bus parking or emergency brakes must be held on by:

• A.

Air pressure.

• B.

A modulating control valve.

• C.

Mechanical force.

Correct Answer
C. Mechanical force.
Explanation
Truck and bus parking or emergency brakes must be held on by mechanical force. This means that the brakes are engaged and held in place by physical mechanisms, such as springs or mechanical linkages, rather than relying on air pressure or a modulating control valve. Mechanical force ensures that the brakes remain engaged even if there is a loss of air pressure or a malfunction in the control system, providing a reliable and fail-safe method for parking or emergency braking.

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• 23.

### You should know your brakes are fading when:

• A.

You have to push the brake pedal harder to control speed on a downgrade.

• B.

The brake pedal feels "spongy" when you apply pressure.

• C.

Your speed increases when you reduce pressure on your brake pedal.

Correct Answer
A. You have to push the brake pedal harder to control speed on a downgrade.
Explanation
When you have to push the brake pedal harder to control speed on a downgrade, it indicates that your brakes are fading. This means that the brakes are losing their effectiveness and are not able to generate enough friction to slow down the vehicle efficiently. As a result, you need to apply more pressure on the brake pedal to compensate for the decreased braking power.

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• 24.

### The air compressor should stop pumping at about _____ psi.

• A.

100

• B.

125

• C.

150

Correct Answer
B. 125
Explanation
The air compressor should stop pumping at about 125 psi because this is the optimal pressure level for most air compressor applications. Going above this pressure can cause damage to the compressor and the equipment being powered by it. Maintaining a pressure of 125 psi ensures efficient operation and prevents unnecessary strain on the compressor.

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• 25.

### The air loss rate for a straight truck or bus with the engine off and the brake on should not be more than:

• A.

1 psi in one minute.

• B.

2 psi in 45 seconds.

• C.

3 psi in one minute.

Correct Answer
C. 3 psi in one minute.
Explanation
The correct answer is 3 psi in one minute. This means that the air loss rate for a straight truck or bus with the engine off and the brake on should not exceed 3 psi within a one-minute period. This is important because excessive air loss can indicate a problem with the air brake system, which could compromise the vehicle's safety and performance. By setting a limit on the air loss rate, it ensures that the system is functioning properly and that any potential issues can be addressed promptly.

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• 26.

### If your truck's air compressor has its own oil supply, when should you first check the oil level?

• A.

Before driving.

• B.

During your first en route inspection.

• C.

Immediately after you stop driving.

Correct Answer
A. Before driving.
Explanation
To ensure the proper functioning of the truck's air compressor, it is important to check the oil level before driving. This is because the air compressor relies on its own oil supply to lubricate its moving parts and prevent excessive wear and tear. By checking the oil level before driving, any deficiencies can be identified and addressed promptly, reducing the risk of damage to the compressor and ensuring its optimal performance throughout the journey. Checking the oil level during the first en route inspection or immediately after stopping driving may be too late and could result in potential issues going unnoticed or worsening.

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• 27.

### The use of air brakes on downgrade is only a supplement to the:

• A.

Use of spring brakes.

• B.

Use of the front brake limiting valve.

• C.

Braking effect of the engine.

Correct Answer
C. Braking effect of the engine.
Explanation
The use of air brakes on a downgrade is only a supplement to the braking effect of the engine. This means that the primary source of braking power on a downhill slope is the engine's braking effect. The air brakes are used as an additional measure to assist in slowing down the vehicle and maintaining control. However, they are not the main source of braking power in this situation. The spring brakes and front brake limiting valve are not mentioned as being directly related to the use of air brakes on a downgrade.

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• 28.

### Your vehicle has a dual air brake system. If a low air pressure warning comes on for the second system, you should:

• A.

Stop the vehicle and continue only when the system is fixed.

• B.

Reduce your speed, and test the remaining system while driving.

• C.

Reduce your speed, and drive to the nearest garage for repairs.

Correct Answer
A. Stop the vehicle and continue only when the system is fixed.
Explanation
If a low air pressure warning comes on for the second system in a dual air brake system, it is important to stop the vehicle and continue only when the system is fixed. This is because the dual air brake system is designed to provide redundancy and ensure proper braking even if one system fails. If the second system is also experiencing low air pressure, it indicates a serious issue that needs to be addressed before continuing to drive. Continuing to drive without fixing the system can compromise the braking ability of the vehicle and lead to accidents.

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• 29.

### All air brake equipped vehicles have:

• A.

An air supply pressure gauge.

• B.

An air use gauge.

• C.

A backup hydraulic system.

Correct Answer
A. An air supply pressure gauge.
Explanation
All air brake equipped vehicles have an air supply pressure gauge because it is essential to monitor the pressure in the air brake system. This gauge allows the driver to ensure that there is sufficient air pressure to operate the brakes effectively. Without this gauge, it would be difficult to determine if there is a problem with the air supply, such as a leak or a malfunctioning compressor. Therefore, an air supply pressure gauge is a crucial component in air brake equipped vehicles.

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• 30.

### The application pressure gauge shows how much air pressure you:

• A.

Have in the air tanks.

• B.

Have in the modulating control valve.

• C.

Are applying to the brakes.

Correct Answer
C. Are applying to the brakes.
Explanation
The correct answer is "Are applying to the brakes." This is because the application pressure gauge is specifically designed to measure the amount of air pressure that is being applied to the brakes. It is not meant to measure the air pressure in the air tanks or in the modulating control valve. Therefore, the correct answer is that the application pressure gauge shows how much air pressure is being applied to the brakes.

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Our quizzes are rigorously reviewed, monitored and continuously updated by our expert board to maintain accuracy, relevance, and timeliness.

• Current Version
• Mar 22, 2023
Quiz Edited by
ProProfs Editorial Team
• Jan 19, 2015
Quiz Created by
Devin Hutchings

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