How to Adjust the Brakes on a Peterbilt

Most all Peterbilt make and model trucks come equipped with adjustable slack adjusters. The slack adjusters are the main components that compress and retract the brake shoes away from the brake drums. When air is applied to the brakes, the slack adjuster compresses the brake shoes to the brake drum. When the air is released from the air brakes, the brake shoes retract from the brake drums. Excessive use will cause the brake shoes to wear down and come out of adjustment. The brake shoes will then need to be adjusted to keep the brakes working properly.

Instructions

1

Pull the Peterbilt truck onto a flat surface and apply the air brakes. Position the wheel chocks in the front and back of both rear wheels. Release the air brakes.

2

Slide under the rear of the Peterbilt truck and locate the two slack adjusters that are mounted to the rear axle. Each slack adjuster has an adjustment bolt on the rear. Position a ratchet and a socket onto the adjustment bolt of the driver side rear slack adjuster. Push in on the head of the ratchet to release the locking spring. Turn the adjustment bolt clockwise one full turn. Shine the flashlight through the back of the wheel hub to see if the brakes are compressing toward the brake drum. If not, turn the adjustment bolt counter-clockwise to compress the brake shoes to the brake drum.

3

Continue to turn the adjustment bolt in the direction that compresses the brake shoes to the surface of the brake drum. Once that the adjustment bolt stops turning, shine the flashlight through the rear of the wheel hub again to ensure that the brake shoes are fully compressed to the surface of the brake drum. Turn the adjustment bolt in the opposite direction one-quarter to one-half of a turn to position the brake shoes to the proper distance from the surface of the brake drums.

4

Crank the engine up and let the air pressure build up to between 80 p.s.i and 120 p.s.i. Apply the air brakes for about ten seconds and then release the air brakes. Slide back under the rear of the truck and shine the flashlight through the rear of the wheel hub to ensure that the brake shoes have remained at the proper position from the surface of the brake drum.

5

Move to the passenger side rear slack adjuster and repeat the same process as outlined above to adjust the Peterbilt truck brakes.