Instructions

Air Brakes

This endorsement is required for driving a vehicle with air brakes. To receive this endorsement, applicants must pass a written test. The test consists of 25 multiple choice.. Read More

This endorsement is required for driving a vehicle with air brakes. To receive this endorsement, applicants must pass a written test. The test consists of 25 multiple choice questions. Each question has three answer choices. To pass, the applicant must answer at least 20 questions correctly. Test questions come from the Iowa Commercial Driver License Manual. Questions come from the chapter covering: Air Brakes. The Air Brakes endorsement may be used with the Class A, B or C CDL.

Number of Question 25

Passing Score 20

19. 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.

20. 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.

21. 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.

22. 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.

23. Having ABS on only one axle:

Can be dangerous.

Still allows you additional control when braking.

Slows the vehicle, but cannot stop it.

If you have an Anti-Lock Braking System (ABS) equipped on only the tractor, only the trailer, or only one axle, you will still have more control over the vehicle when braking than you would without ABS. You should brake normally.

24. 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.

25. 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.

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