GM 84497385 Cylinder Assembly, Brk Mas

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Remove the nuts attaching the master cylinder to the power booster, and carefully pull the master cylinder off the studs.

To remove the brake master cylinder, start by disconnecting the cable from the negative terminal of the battery. Then, unplug the electrical connector for the fluid level warning switch. Next, remove as much fluid as possible from the reservoir using a suction gun, large syringe, or poultry baster (but never use the baster for food preparation again). Place rags under the fittings and prepare caps or plastic bags to cover the ends of the lines once they're disconnected to prevent brake fluid from damaging the paint. Loosen the fittings at the ends of the brake lines where they enter the brake master cylinder using a flare-nut wrench. Pull the brake lines away from the brake master cylinder and plug the ends to prevent contamination. Remove the nuts attaching the brake master cylinder to the power booster and carefully pull the brake master cylinder off the studs. To install the new brake master cylinder, bench bleed it first by mounting it in a vise and attaching brake master cylinder bleeder tubes to the outlet ports. Fill the reservoir with the recommended brake fluid and slowly push the pistons into the brake master cylinder to expel air. Repeat until no more air bubbles are present. Remove the bleed tubes and install plugs in the open ports. Install the brake master cylinder over the studs on the power brake booster and tighten the attaching nuts finger tight. Thread the brake line fittings into the brake master cylinder, ensuring not to strip the threads. Tighten the mounting nuts and brake line fittings securely. Fill the brake master cylinder reservoir with fluid and bleed the lines at the brake master cylinder, followed by bleeding the rest of the brake system. To replace the reservoir or O-rings, remove as much fluid as possible from the reservoir and place rags under the brake master cylinder. Use a hammer and small punch to drive out the roll pins that retain the reservoir. Pull the reservoir out and replace the O-rings if necessary. Lubricate the reservoir O-rings with clean brake fluid and press the reservoir into place, securing it with new roll pins. Refill the reservoir with the recommended brake fluid, check for leaks, and bleed the brake master cylinder.