GMC 84644599 Cylinder Kit, Brk Mas

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To remove the brake master cylinder, start by turning off the ignition switch and removing the air filter element. If necessary, remove the air filter cover and outlet duct as well. Use a syringe or turkey baster to remove as much fluid as possible from the reservoir. Disconnect the brake booster check valve and the electrical connector at the brake fluid level switch. Remove the windshield washer fluid heater if it is equipped. Place rags under the fluid fittings and prepare caps or plastic bags to cover the ends of the lines. Clean off any dirt or debris from around the brake line fittings. Loosen the fittings at the ends of the brake lines 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. If installing a new brake master cylinder, spread the tabs on the bottom of the reservoir, lubricate new reservoir seals with brake fluid, and secure the reservoir to the new brake master cylinder. To install the new brake master cylinder, bench bleed it first by mounting it in a vise and attaching bleeder tubes to the outlet ports. Fill the reservoir with 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. Thread the brake line fittings into the brake master cylinder and tighten them securely. Fill the reservoir with fluid and bleed the brake master cylinder and brake system. Test the brake system before placing the vehicle into normal service.