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 or four answer choices. To pass, the applicant must answer at least 20 questions correctly. Test questions come from the Maryland Commercial Driver Guide. 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

1. To inspect slack adjusters on S-cam brakes, you need to:

Park on a hill and test the brakes.

Put on gloves and push in the slack adjusters.

Remove the drum and look inside.

Chock the wheels and disengage the parking brake.

Check each slack adjuster after parking on level ground, setting wheel chocks, and disengaging the parking brake. Pull the slack adjusters to make sure they do not move more than about one inch from where the push rod is attached. If they move more than one inch, they may be out of adjustment and will need to be fixed.

2. Failing to drain the tanks in an air brake system can result in:

Water freezing and causing brake failure.

Squishy brakes.

Too much air collecting.

Too much fuel being carried.

In an air brake system, the air storage tanks must be drained to remove accumulated water and compressor oil. Failing to do this can cause damage. For example, water that has built up in the system could freeze in cold weather and cause brake failure.

3. 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.

4. What is brake lag?

The time required for the brakes to work after the brake pedal is pressed

The distance between the brake pedal and the floor

The amount of air pressure used to stop the vehicle

Because air takes time to flow through the air lines to the brakes, air brakes cannot begin working instantly. There is often a brake lag of at least one-half of a second between the moment the brake pedal is pressed and the moment the brakes begin to work.

5. 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.

80 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.

6. 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.

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