How do you replace proportioning valve on 91 Toyota pickup?

To replace the proportioning valve on a 1991 Toyota pickup, first ensure the vehicle is safely lifted and supported, and then disconnect the battery. Drain the brake fluid from the master cylinder and remove the brake lines from the old proportioning valve, taking care to note their positions. Unbolt the old valve from its mounting, then install the new valve in the same position, reconnect the brake lines, and refill the brake fluid. Finally, bleed the brake system to remove any air before reconnecting the battery and testing the brakes.