GM 19209255
Master Cylinder

The procedure to fix the Brake Master Cylinder starts with mounting it in a bench vise to access the primary Piston. Mount suitable fittings that match the required flare seat at the master cylinder ports to allow you to attach hoses. Link transparent hoses to these fittings and bring them into the master cylinder reservoir space. Put delco supreme 11 brake fluid gm part number 12377967 or its equivalent dot-3 fluid into the reservoir from a sanitation-sealed container until the hoses and fluid bottom reach the halfway mark. Using a round smooth tool press and release the Piston into the primary chamber twice as depth reaches about 25 mm (1 in). Repeat until no more air bubbles appear from the ports and the tool loses its natural return path. Keep pushing the Piston movement until the ports release fluid without showing air pockets inside the system. Take off the transparent hoses from the reservoir then put back the master cylinder reservoir cap and diaphragm before separating the hoses from their connections at the ports while keeping the master cylinder wrapped with a clean cloth to avoid spills.

Use a smooth, round-ended tool to depress the primary piston and remove the piston retainer, followed by the primary piston assembly from the cylinder bore.

Remove the reservoir from the master cylinder.

Clean with denatured alcohol and inspect for cracks, scoring, pitting, or corrosion.

Remove the reservoir from the master cylinder.

Plug the open brake pipe fitting ends, remove the two master cylinder mounting nuts, and take out the master cylinder.

Fill the reservoir to at least the halfway point with Delco Supreme 11 or equivalent DOT-3 brake fluid, ensuring the ends of the hoses are fully submerged.

Dry all components with non-lubricated, filtered air, then lubricate the master cylinder bore, secondary piston, return spring, and all overhaul components with Delco Supreme II or equivalent DOT-3 brake fluid.

Plug the open brake pipe fitting ends, remove the 2 master cylinder mounting nuts, and take out the master cylinder.