An automatic slack adjuster is the main component that keeps the brake shoes at the proper distance from the surface of the brake drums. As the brake shoes and the brake drums wear down, the automatic slack adjusters will automatically adjust the brake shoes so that the shoes remain at the proper distance from the drums. If the brake shoes lock up within the brake drums, the automatic slack adjusters must be manually adjusted to release the brakes.
Apply the air brakes to the brake shoes by pulling out on the air brake knob. Walk back to the rear axles and place the wheel chocks in front of both rear wheels and behind both rear wheels.
Release the air brakes by pushing in on the air brake knob. Slide under the rear of the vehicle and locate the automatic slack adjusters. The slack adjusters are mounted to each side of both rear axles. The automatic slack adjusters have a release button on the side of the adjuster and an adjustment bolt head on the bottom of the adjuster.
Choose one of the slack adjusters to adjust first. Slide the flat tip of a flathead screwdriver underneath the release button on the side of the slack adjuster. Pry the release button out with the screwdriver and hold it out with one hand.
Turn the adjustment bolt on the bottom of the slack adjuster counterclockwise with a ratchet and a eight-point socket to move the brake shoes toward the surface of the brake drums. Use the flashlight to shine through the back side of the brake shoe plate to see the brake shoes and the brake drum. Continue turning the adjustment bolt counterclockwise until the brake shoes are fully applied to the surface of the brake drum.
Back off the brake shoes by turning the adjustment bolt one-half a full turn clockwise to set the brake shoes to the proper distance away from the surface of the brake drum. This will put the brake shoes about one-eighth of an inch away from the inside surface of the brake drum Use the flashlight to ensure that the shoes are about one-eighth of an inch away from the drum.
Remove the screwdriver out from under the release button. Pull the socket and ratchet off the adjustment bolt. Move to the other three automatic slack adjusters and repeat the same process as outlined in the steps above to properly reset the slack adjusters so that the brake shoes are at the proper distance from the brake drums.
