GM 18020180 Valve Asm

The brake proportioning valves enhance front-to-rear brake balance during severe brake applications, which shift some of the vehicle's rear weight to the front wheels, potentially leading to decreased braking efficiency and rear wheel lockup. These valves limit pressure to the rear brakes to mitigate this issue. For removal and installation without Anti-Lock brakes on 1990 vehicles, disconnect the negative battery cable, detach the brake lines from the proportioning valves, and remove the valve and O-rings from the master cylinder. When installing, lubricate new O-rings and valve threads with clean brake fluid, secure the valves to the master cylinder, reconnect the brake lines, and bleed the brake system. For 1991-93 DeVille and Fleetwood models, remove the master cylinder, clamp it in a vise, and carefully tap back the spring pins to detach the reservoir. Inspect and clean all parts, lubricate new seals and O-rings, and reassemble the components before reinstalling the master cylinder and bleeding the system. For models with Anti-Lock brakes from 1990, depressurize the hydraulic system by pumping the brake pedal multiple times, then disconnect the brake lines and remove the proportioning valve. Reinstall the valve, connect the lines, and bleed the system. For 1991-98 models, raise the vehicle, clean connections, disconnect the lines, and remove the valve before reinstalling and bleeding the system.