GMC 18030604 Cylinder Asm,Brake Master

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Before deciding on overhauling the Brake Master Cylinder, it's important to check the availability and cost of a new or factory rebuilt unit, as well as the availability of a rebuild kit. To begin the removal process, place rags under the brake line fittings and prepare caps or plastic bags to cover the ends of the lines once they're disconnected, as brake fluid can damage paint. Loosen the tube nuts at the ends of the brake lines using a flare-nut wrench to prevent rounding off the flats on the nuts. Unbolt the isolation/dump valve and RWAL module mounting bracket, then plug the brake line ends to prevent contamination. Remove the two Brake Master Cylinder mounting nuts and move the bracket aside slightly, taking care not to kink the hydraulic lines. Remove the Brake Master Cylinder from the vehicle and discard any remaining fluid in the reservoir after removing the reservoir cover and diaphragm. To overhaul and install the Brake Master Cylinder, mount it in a padded vise and remove the primary piston lock-ring by depressing the piston and prying the ring out. Remove the primary and secondary piston assemblies, as well as the reservoir and grommets. Inspect the cylinder bore for damage, and if found, replace the Brake Master Cylinder body. Lubricate and press the new reservoir grommets into place, then attach the Brake Master Cylinder body to the reservoir using a rocking motion. Install new seals on the secondary piston assembly, and lubricate the cylinder bore before installing the spring and secondary piston assembly. Install the primary piston assembly and lock-ring, and inspect the reservoir cover and diaphragm, replacing any damaged parts. The entire hydraulic system must be bled whenever the Brake Master Cylinder is removed, and this can be facilitated by bench bleeding the Brake Master Cylinder before installation. Fill the reservoirs with brake fluid, hold fingers tightly over the holes where the brake lines connect, and stroke the piston several times to expel air. Carefully install the Brake Master Cylinder by reversing the removal steps and bleed the brake system as described in Section 15.