GM 19236088
Master Cylinder Assembly

You should perform bench bleeding on the Brake Master Cylinder before vehicle installation because it will shorten the subsequent brake hydraulic system bleeding process. The first step requires you to plug the outlet ports before positioning the Brake Master Cylinder in a vise with a downward slope at the front end. Stroke the primary Piston using a smooth round-end tool to achieve 25 mm (1 inch) motion in multiple repetitions when filling the reservoir with brake fluid. The Piston movement stops before reaching maximum due to air exiting the system. Place the master cylinder back into the vise but this time position it at a slight upward tilt and repeat the multi-stroke procedure on the primary Piston for about 25 mm (1 inch). Determine the vise losenanny alignment at a flat position while allowing independent opening of outlet port plugs. Proceed to push the Piston into the bore which creates air pressure in the cylinder until the plugs are tight then release the Piston to prevent air ingress before filling the master cylinder with clean brake fluid to continue with standard bleeding protocols through manual or pressure bleeding procedures.

Clean the interior and exterior of the master cylinder, secondary piston, and return spring using denatured alcohol or an equivalent, and inspect for cracks, scoring, pitting, or corrosion.

Clean all parts using denatured alcohol for metal components and clean brake fluid for rubber parts, inspecting the diaphragm for damage and the cylinder bore for scoring or corrosion.

Bench bleed the master cylinder, then attach it to the brake booster.

Drain all brake fluid from the master cylinder reservoir.

Remove the Brake Master Cylinder Mounting Nuts that secure the brake master cylinder to the brake booster and take out the brake master cylinder from the brake booster.

Clean the area around the reservoir cap.