By replacing the bleeder at each corner with a brake gauge, side-to-side pressure variations point to a pinch, block, or leak in the lines, and front-to-rear variations help narrow down biasing issues. Disc systems typically need 800-1,200 psi up front and 750 psi in the rear to actuate pistons; drums require as little as 400 psi for wheel cylinders to spread shoes. On this four-disc-converted manual-braked CJ, each corner spiked under 500 psi during brake-pumping. Pressure dissipated with the pedal depressed, indicating a bad master cylinder. An MC rebuild spiked the pressure to 1,200 in front and 700 in the rear without an adjustable proportioning valve.