GM 20845347 Cylinder Assembly, Brake Master

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To remove the brake master cylinder, first disconnect the cable from the negative battery terminal and unplug the electrical connector for the fluid level warning switch. Remove as much fluid as possible from the reservoir and prepare caps or plastic bags to cover the ends of the lines once they're disconnected. Loosen the fittings at the ends of the brake lines where they enter the brake master cylinder and pull the brake lines away from the brake master cylinder, plugging the ends to prevent contamination. Remove the nuts attaching the brake master cylinder to the power booster and pull the brake master cylinder off the studs. To install the new brake master cylinder, bench bleed it before installing it by mounting it in a vise and attaching a pair of brake master cylinder bleeder tubes to the outlet ports. Fill the reservoir with brake fluid of the recommended type and slowly push the pistons into the brake master cylinder until no more air bubbles are present. Remove the bleed tubes and install plugs in the open ports to prevent fluid leakage and air from entering. Replace the o-ring seal on the end of the brake master cylinder and install it to the booster, leaving the mounting nuts finger tight for now. Thread the brake line fittings into the brake master cylinder and tighten the mounting nuts to the torque specifications. Fill the brake master cylinder reservoir with fluid, then bleed the lines at the brake master cylinder, followed by bleeding the remainder of the brake system. Confirm that the brakes are fully operational before resuming normal driving.

Disconnect the cable from the negative battery terminal and unplug the electrical connector for the fluid level warning switch. Remove as much fluid as possible from the reservoir and prepare caps or plastic bags to cover the ends of the lines once they're disconnected.