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How to Release Air Brakes

by Gregory Crews

The air brakes in a truck work in the opposite manner as hydraulic brakes. When you press the brakes on a hydraulic system, this pushes the calipers to the rotor, causing the truck to stop. The air brakes work the exact opposite. The air in the brake system actually pushes the calipers away from the drums. When you press the brake pedal, this releases the air from the brake lines and applies pressure to the drum. This is the reason it is essential to have adequate air supply to the brake lines.


Start the truck by turning the ignition key to the "Start" position. Some trucks have a pushbutton ignition and will require turning the key to the "On" position then pressing the button to start the truck.


Locate the air pressure gauge on the dash. This gauge will be a small gauge labeled "Air Pressure."


Observe the needle in the air pressure gauge as it rises while the truck is idling. An indicator will make a buzzing sound as well.


Allow the air pressure to build to 120 pounds of air. The buzzing will stop at 60 pounds. You will hear the air bags settle under the truck once the pressure stops building.


Press the yellow button labeled "Parking" while your foot is on the brake pedal. This will release the truck air brakes.


Press in the red button labeled "Trailer" if a trailer is attached. This will release the trailer brakes. Keep your foot on the brake pedal to prevent the truck from rolling.


  • The buttons will not move if the air supply has not built pressure.

About the Author

Gregory Crews has been in the film industry for three years and has appeared in more than 38 major motion pictures and 16 television shows. He also writes detailed automotive tutorials. His expertise in the automotive industry has given him the skills to write detailed technical instructional articles.

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