GM 19209259
Master Cylinder

Place the Brake Master Cylinder flange in a bench vise correctly making the back of the primary Piston visible. Put suitable flare-seat fitting connections on the master cylinder ports after you take out the diaphragm and reservoir cap. The fittings need to match the hoses. Seal these fittings by attaching transparent hoses and placing their ends into the master cylinder reservoir. Add delco supreme 116 (GM P/N 12377967, Canadian P/N 992667) dot-3 brake fluid up to the middle mark of the reservoir from a sealed fluid can, placing the hose ends fully in the fluid. Press the Piston with a rounded tool then release it up to 25 mm (1 inch) multiple times to check fluid flow from the ports. The resistance increases as you push the primary Piston deeper because you release compressed air from this Piston suite. Press the primary Piston multiple times while monitoring port fluid stream for bubbles until the ports deliver fluid easily without air bubbles. After fluid movement ends put the hoses back into the reservoir space and replace the master cylinder cap before disconnecting each port connection piece and laying the master cylinder onto absorbent material.

Before starting the Brake Master Cylinder replacement process disconnect the electrical connector from the brake fluid sensor and then disconnect the brake lines from the master cylinder. Insert rubber caps on the pipe ends to prevent brake fluid loss. First you close the brake pipe ports then remove the master cylinder mounting nuts to take out the part from the vehicle. Empty every brake fluid from the master cylinder storage tank. Before adding the master cylinder to the Brake Booster you should drain brake fluid from the system while bleeding the cylinder on a workbench. Fasten the master cylinder nuts with 29 n.m torque measurements (21 lb ft). Place the brake pipe plugs away while connecting the brake pipes to the master cylinder. Fully tighten the brake pipe screws at the master cylinder to reach 24 n.m (18 lb ft). Connect the electrical unit to the brake fluid sensor and complete hydraulic brake system bleeding.

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

Remove the plugs from the brake pipes and connect them to the master cylinder, tightening the brake pipe fittings to 24 N.m (18 lb ft).

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

Reconnect the electrical connector to the brake fluid level sensor and bleed the hydraulic brake system.

Disconnect the electrical connector from the brake fluid level sensor.

Drain all brake fluid from the master cylinder reservoir.

Plug the cylinder inlet ports and rear outlet port, then apply low pressure, non-lubricated, filtered air into the front outlet port to remove the secondary piston along with the primary and secondary seals and the return spring.