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As self-adjusting air brakes age and wear, they will need to be adjusted. These brakes will only self-adjust within a certain tolerance; When the air brakes exceed this tolerance, they must be adjusted manually. As the air brake ages, the rubber in the brake chamber will stretch and become more brittle. As such, the brake arm will have to travel further to activate the brakes. The longer the brake arm has to travel, the longer it will take to stop the vehicle.
Jack up the vehicle. Place it on jack stands. If the vehicle is large enough, you may not have to lift it. If you do not lift the vehicle, chock the tires.
Look next to a rear wheel and find the brake chamber. The push rod exits the rear of the brake chamber and enters the brake chamber when the brake is pressed. If you are having trouble finding the brake chamber, have an assistant press the brakes and look for the push rod that goes into the brake chamber.
Look at the back of the push rod to find the adjusting nut. Turn the adjusting nut in the direction that you can turn it freely. The trim will rotate freely in only one direction and move in the other. Turn the nut until the brake shoes are against the drum and the nut does not turn further.
Turn the nut in the other direction so you can hear it creak as you turn. Turn the nut 1-1 / 2 full turns.
Measure the distance the push arm travels to the brake chamber. Have your assistant press the brakes while you measure the distance you travel. The push arm should travel between 1.25 and 1.5 inches, but no more than 2 inches.
- If your vehicle is raised, spin the tire to see if the shoe touches the drum.
- If the pushrod drifts more than 2 inches, have a professional mechanic repair the vehicle.
Articles will need
- Open end wrench set
- Jack stand or wheel chocks