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How to Adjust Self Adjusting Air Brakes

by BretN

As self adjusting air brakes age and wear they will require adjustment. These brakes will only self-adjust within a certain tolerance; when the air brakes go beyond this tolerance they must be adjusted manually. As the air brake ages, rubber in the brake chamber will stretch and become more brittle. As such, the brake arm will have to travel further to engage the brakes. The longer the brake arm has to travel, the longer it will take to stop the vehicle.

Jack the vehicle up with the jack. Place it on jack stands. If the vehicle is large enough, you may not have to jack it up. If you do not jack the vehicle up, chock the tires.

Look next to a rear wheel and find the brake chamber. The push rod comes out the back of the brake chamber and goes into the brake chamber when the brake is pressed. If you have trouble finding the brake chamber, have an assistant press the brakes and look for the push rod going into the brake chamber.

Look at the back of the push rod to find the adjustment nut. Turn the adjustment nut in the direction that you can turn it freely. The adjustment will turn freely in only one direction and will ratchet in the other. Turn the nut until the brake shoes are against the drum and the nut will not turn any more.

Turn the nut in the other direction so that you hear it ratcheting as you turn. Turn the nut 1-1/2 full turns.

Measure the distance the push arm travels into the brake chamber. Have your assistant push on the brakes while you measure the distance it travels. The push arm should travel between 1.25 and 1.5 inches, but no more than 2 inches.

Tip

  • If your vehicle is jacked up, spin the tire to see if the shoe touches the drum.

Warning

  • If the push rod travels more than 2 inches, have the vehicle repaired by a professional mechanic.

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