GM 18042801
Master Cylinder

Before working on the Brake Master Cylinder make sure to follow brake fluid irritant caution and notice the consequences of brake fluid on the paint and electrical items. Use clean sealed containers of delco supreme 115 brake fluid gm p/n 12377967 or equivalent product type dot-3 to add fluid since other products harm internal rubber components. Put the Brake Master Cylinder mounting flange into a bench vise where the rear of its primary Piston will be easy to reach. Drain the master cylinder reservoir fluids through its diaphragm and place industry-standard connectors onto port openings for hose connection. Route transparent hoses into the reservoir from its fittings and fill the system halfway with recommended brake fluid. Put both hose ends into brake fluid so you can push and release the primary Piston through its travel of 25 mm with a smooth tool to check for fluid flow from the ports. When air leaves the pistons both pressure and Piston travel grow more difficult. Keep working to make the ports emit fluid without bubble formation. Take off the transparent hoses from the reservoir; put back on the reservoir cap and diaphragm followed by removing the fittings from the master cylinder ports while using a clean shop cloth to protect the vise setup.

The primary piston assembly, piston retainer, and seals from the secondary piston.

Disconnect the electrical connector from the Brake Fluid Level sensor and the brake pipes from the master cylinder.

Reconnect the electrical connector to the low brake fluid level sensor switch.

Install the lubricated return spring and secondary piston assembly into the cylinder bore, followed by the lubricated new primary piston assembly.

Bench bleed the master cylinder, then install it to the vacuum brake booster and position the proportioning valve assembly bracket or the antilock brake modulator bracket onto the brake booster studs.

Delco Supreme II, GM P/N 12377967 (Canadian P/N 992667), or equivalent DOT-3 brake fluid from a clean, sealed container.