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 questions. Each question has three answer choices. To pass, the applicant must answer at least 20 questions correctly. Test questions come from the Oklahoma 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
Passing Score
19. An emergency brake must be controlled by:
Explanation
All trucks, truck tractors, and buses must be equipped with emergency brakes and parking brakes. Because air pressure can eventually leak away, emergency and parking brakes should be held on by mechanical force.
20. If you are braking on dry pavement while traveling at 55 mph, how much distance will brake lag add to your overall stopping distance?
Explanation
The total stopping distance for vehicles equipped with air brakes is made up of four factors: perception distance, reaction distance, brake lag distance, and braking distance. When braking at a speed of 55 mph while driving on dry pavement, the brake lag can add around 32 feet to the vehicle's total stopping distance.
21. When experiencing cold weather, be sure to check your vehicle's alcohol evaporator:
Explanation
An alcohol evaporator can help prevent ice from building up in an air brake system. In cold weather, the evaporator should be checked and refilled every day.
22. If the low air pressure warning signal comes on, you should:
Explanation
If the low air pressure warning signal comes on while you are driving a vehicle with air brakes, you should immediately bring the vehicle to a safe stop while you are still able to control the brakes. Inspect and repair the brakes as soon as possible.
23. What is often found in compressed air?
Explanation
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.
24. If an air compressor is belt-driven, the belt should be routinely checked to ensure that it is:
Explanation
If your vehicle has air brakes, the air compressor drive belt should be checked before each drive. Check the tightness of the belt and verify that it is in good condition.
25. What is brake lag?
Explanation
