If you are using Cadillac Eldorado-style rear calipers (as we did), there are some important things you should know. These rear calipers adjust off the parking brake, which is incorporated into the caliper. You must set the parking brake every time you park the car so that you utilize a one-way clutch inside the caliper piston. When the parking brake is applied, the clutch senses when there is a 0.030-inch or greater clearance between the friction material and the rotor on the inboard side. When there is in excess of 0.030 inch, the clutch turns inside the piston, adjusting it out, keeping the rear brakes adjusted. If you do not set your parking brake every time, you will start to lose brake pedal (low and spongy) and the adjuster mechanism will not work.
Showstopper - Technical Article - Chevy High Performance Magazine
Adding a Master Power Disc Brake Kit