GM 18040249 CYLINDER

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To remove the brake master cylinder, start by placing rags under the brake line fittings and preparing caps or plastic bags to cover the ends of the lines once they're disconnected. Then, use a flare-nut wrench to loosen the tube nuts at the ends of the brake lines where they enter the brake master cylinder. Pull the brake lines away slightly and plug the ends to prevent contamination. If the vehicle has a Rear-Wheel Anti-Lock (RWAL) brake system, remove the RWAL module. Remove the two brake master cylinder mounting nuts and set aside the bracket for the RWAL module and isolation/dump valve. Remove the brake master cylinder from the vehicle and discard any remaining fluid in the reservoir. To overhaul the brake master cylinder, mount it in a padded vise and remove the primary piston lock ring. Take out the primary and secondary piston assemblies from the cylinder bore, and remove the reservoir and grommets. Do not attempt to remove the quick take-up valve. Inspect the cylinder bore for damage and replace if necessary. Lubricate and install new reservoir grommets, then press the brake master cylinder body onto the reservoir. Install new secondary seals on the second piston assembly. For installation, attach the spring seat to the secondary piston assembly and install the primary piston assembly in the cylinder bore. Inspect and replace any damaged reservoir cover and diaphragm. Bench bleed the brake master cylinder by filling it with brake fluid and holding your fingers tightly over the holes where the brake lines normally connect. Stroke the piston several times to expel air. Carefully install the brake master cylinder by reversing the removal steps and bleed the brake system.

Remove the two master cylinder mounting nuts and set aside the bracket for the RWAL module and isolation/dump valve. Then, remove the master cylinder from the vehicle and discard any remaining fluid in the reservoir.