Wisconsin CDL Air Brakes Practice Test

Using the brakes creates heat. If too much heat is produced:

• The brakes may not work.
• The brakes may squeak more than usual.
• The brakes will brake unevenly.

Brakes are designed to take a lot of heat, but drivers should not rely solely on the brakes to slow their vehicle. Brakes may fade and lose their ability to slow down the vehicle if they become too hot, so drivers should also rely on the engine braking effect.

What do the two systems of a dual air brake system share?

• Hoses
• An air compressor
• Air tanks

Both systems in a dual air brake systems share a single air compressor. If the air compressor is damaged, neither system will be able to operate properly.

What do air brakes use to make the brakes work?

• Compressed air
• Outside air
• Non-compressed air

Many large CMVs are equipped with air brakes. An air braking system uses compressed air to operate.

What is removed when an air tank is drained?

• Water and oil
• Ammonia
• Liquid cleaners

In an air brake system, air tanks have drains to remove accumulations of water and compressor oil. Allowing water and oil to accumulate in the system could cause damage to the brakes.

If the low air pressure warning signal comes on in a vehicle with air brakes, the driver should:

• Test the brakes while driving, but continue driving if nothing seems wrong.
• Immediately stop driving.
• Drive with the hazard lights activated.

If the low air pressure warning signal comes on while you are operating a vehicle with air brakes, you should stop and safely park the vehicle as soon as possible. It is essential that you are able to stop safely while you still have some braking power remaining.

Air tank drains:

• Should not be used in cold weather.
• Are helpful to remove water and oil from the air tanks.
• Are used to move air to the brakes.

Compressed air in an air brake system usually has a certain amount of water and oil in it. This can harm the system if allowed to accumulate. Air tanks have drain valves to aid in removing water and oil from the compressed air.

Air pressure should build up in a single air system within:

• 15 minutes.
• 12 minutes.
• Three minutes.

In single air systems, air pressure should build from approximately 50 to 90 psi within three minutes.

In a dual air brake system, a leak in one system:

• Always means there are leaks in both systems.
• May not affect the other system.
• Is not something to worry about.

A dual air brake system is made up of two separate air brake systems. If there is an air leak in one system, it may not affect the other.

When you press the brake pedal in a vehicle with S-cam brakes, air pressure pushes out the rod and moves the:

• Slack adjuster.
• Axle.
• Brake drum.

When pressing the brake pedal in a vehicle with S-cam brakes, air will enter the brake chambers. The added air pressure will push out the rods and move slack adjusters, twisting the brake camshafts.

An air compressor governor will stop the compressor from pumping air once the air tanks have an air pressure level of:

• 125 psi.
• 100 psi.
• 150 psi.

An air compressor governor will stop the compressor from pumping air once the air tanks are at an air pressure level of 125 psi. This air pressure level is referred to as the "cut-out" level.

If the safety relief valve in the air brake system releases air:

• The compressor needs more air.
• The air pressure has become too high.
• The brakes are fully operational.

An air brake system has a safety relief valve, which releases air from the tanks if the pressure gets too high. If the valve must operate, something in the system is wrong and should be addressed by a mechanic.

The parking brake in a newer vehicle is applied by:

• Moving a lever to the right.
• Pushing a yellow, diamond-shaped knob.
• Pulling a yellow, diamond-shaped knob.

In newer vehicles with air brakes, the parking brake is controlled by a yellow, diamond-shaped knob. The driver should pull the knob outward to apply the parking brakes and push the knob inward to release them.

If the safety relief valve in an air brake system is releasing air:

• You should not be concerned as this is a normal process.
• There is something wrong with the brakes.
• The valve is operational.

The safety relief valve in an air brake system releases air if necessary to prevent pressure in the system from becoming too high. If the valve starts releasing air, there is something wrong. Have a mechanic fix the problem.

During an applied leakage test, the maximum leakage rate for a single vehicle with air brakes is:

• 3 psi in one minute.
• 6 psi in one minute.
• 8 psi in one minute.

It is important to know the maximum air loss rate that is safe for your specific vehicle. A single vehicle with air brakes should have a leakage rate no higher than 3 psi in a minute during an applied leakage test.

A driver can rely on front wheel braking to work:

• On dry roadways only.
• Under all conditions.
• Under all conditions, except for snow.

Front wheel braking is effective under all road conditions. It is unlikely that you will experience a front wheel skid, even on ice.

When leaving your vehicle unattended:

• The parking brake should be used.
• The parking brake only needs to be used if the vehicle is parked on a slope.
• The parking brake should not be used, as it can damage the tires.

In general, you should always use the parking brake when parking your vehicle. However, you should not apply the parking brake if your brakes are very hot or if your brakes are wet and temperatures are below freezing.

The ____ are activated by an electric switch that is triggered by the brake pedal.

• Headlights
• Turn signals
• Brake lights

In a vehicle with air brakes, the brake lights are activated when the brake pedal is pushed and air pressure moves an electric switch. With the application of air pressure, the switch will then turn on the brake lights.

The air pressure in a dual air brake system should build from 85 to 100 psi within:

• Two minutes.
• 15 seconds.
• 45 seconds.

When inspecting a vehicle with a dual air brake system, you should wait for air pressure to build from 85 to 100 psi in both the primary and secondary systems. This should take about 45 seconds.

You should ____ if the low pressure warning signal activates while you are driving.

• Stop where you are and park
• Exit the roadway as soon as safely possible
• Continue driving normally

If the low pressure warning signal activates while you are driving, it is important that you safely exit the roadway as soon as possible and park your vehicle. If the air pressure gets too low, the brakes will no longer work well enough for you to stop safely.

Braking mechanisms are located ____ a brake drum.

• Outside
• Inside
• Next to

Drum brakes are attached to the wheels and located on the axles of a vehicle. The braking mechanisms that cause the vehicle to stop can be found inside of a drum brake.

An application pressure gauge shows:

• How much air pressure is being applied to the brakes.
• How much air pressure is available.
• How much air pressure is required to stop a vehicle.

If a vehicle is equipped, an application pressure gauge shows how much air pressure is being applied to the brakes. This gauge can help a driver identify if their brakes are beginning to fade.

An air brake-equipped vehicle traveling at a speed of 55 mph under ideal driving conditions will need approximately ____ to come to a complete stop.

• 100 feet
• 250 feet
• 450 feet

A vehicle's total stopping distance is made up of perception distance, reaction distance, brake lag distance, and braking distance. With all of these factors included, an air brake-equipped vehicle traveling at a speed of 55 mph under ideal driving conditions will need approximately 450 feet to come to a complete stop.

When parked on a flat surface, you should:

• Use wheel chocks to prevent your vehicle from moving.
• Not use wheel chocks.
• Use wheel chocks, but only if you have applied the parking brake.

When parking on a level surface, you should use wheel chocks. If the vehicle is not equipped with spring brakes, this is essential to prevent the trailer from moving.

What is often found in compressed air?

• Water
• Cardboard
• Brake fluid

Compressed air in an air brake system usually contains a certain amount of water and compressor oil. The water and oil can damage the brakes if left to accumulate in the system. Tanks must be drained regularly to remove this build-up.

A dual air brake system:

• Consists of two separate air brake systems that share a single set of controls.
• Is a single air brake system with two different sets of controls.
• Consists of one air brake system for the left side of the truck and one system for the right side of the truck, each with its own set of controls.

A dual air brake system is made up of two separate air brake systems. The systems share a single set of brake controls, but each has its own air tanks, hoses, and lines. One system typically operates the regular brakes on the rear axle or axles while the other system operates the regular brakes on the front axle.