The diagram shows the 3 adjustment point brake system and explains the effect of each of the individual adjustments. The anchor pin moves the secondary brake shoe closer or further away from the drum. The eccentric screw positions the primary shoe in a similar manner and the “star wheel” adjustment screw at the bottom of the brake assembly expands both shoes outward as necessary to the proper position. It is essential for smooth braking that the primary and secondary shoes simultaneously move into contact with the brake drum.
Performing all of the adjustments necessary for your particular Pontiac will insure the minimum of lining wear due to full contact with the brake drum, and also that the maximum braking effort is generated. You will definitely notice a difference in the “feel” and amount of brake pedal travel if the brakes are properly adjusted.