The slack adjusters are used to adjust for wear on S-cam air brakes in heavy and medium-size trucks. Although the slack adjusters usually automatically adjust, sometimes they have to be manually adjusted if they are not working properly. This is not a lengthy process, but the adjustment must be done correctly to ensure the brakes work properly on your vehicle.
Secure the vehicle by chocking the wheels to ensure there is no movement during the process.
Inspect the brake system and make sure it is at full pressure. Press the brake pedal and watch that it returns at full pressure. Enact the emergency brake and push in the air valve, which will release the brakes. The air valve is usually a foot pedal located near the brake.
Determine the location where the push rod exits the air brake chamber with a piece of chalk. Twist the push rod gently with a wrench to remove it from the brake chamber. Measure the distance between the brake chamber and the chalk line. If the distance is greater than 3/4 inches, then the slack adjuster needs to be adjusted.
Locate the manual slack adjuster, which is close to the push rod. Turn the slack adjuster with your hand or a wrench if necessary. If air is going into the brake chamber when you press the brakes, you are turning it the wrong way. Reverse the direction you are rotating the slack adjuster if air is going into the brake chamber.
Turn the slack adjuster with a wrench until it is tight and you feel a little resistance. If the slack adjuster cannot be moved anymore, then the brake linings are fitting tight against the drum. Twist the adjuster one-half turn in the other direction to ensure there is the proper distance between the drum and the brake linings.