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.
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.