Q: How Should I Prepare for the Removal of a Master Cylinder?
A: Place newspapers underneath the brake master cylinder before removal to catch any spilled brake fluid. Disconnect the front and rear Brake Lines from the brake master cylinder and plug the lines and brake master cylinder outlets. On manual brake vehicles disconnect the push rod from the pedal linkage. Remove the mounting nuts and detach the brake master cylinder. Remove the cover and gasket and drain the brake fluid into a container. Remove the plugs from the brake master cylinder outlets and drain the remaining brake fluid. Mount the brake master cylinder in a vise equipped with soft jaws. On aluminum body brake master cylinder, remove the black nylon reservoir by rocking it back-and-forth and pulling up on it. Remove the reservoir-to-housing grommets. On all brake master cylinders except the early Bendix models, remove the front piston retainer screw from inside the rear reservoir or directly beneath the reservoir. On early Bendix brake master cylinders, loosen, but do not remove, the piston retainer screw on the flange. Swivel the retainer tab down to release the rear piston assembly. On all brake master cylinders except early Bendix models, push in on the rear piston and remove the piston snap-ring. On early Bendix models, remove the front piston retaining screw located between the brake line outlets. Remove the rear piston assembly from the brake master cylinder bore. Tap the open end of the brake master cylinder on the workbench to dislodge the front piston assembly. Remove the front piston and spring from the bore. On cast iron brake master cylinders, install an EZ out or metal screw in the tube seats. Remove and discard the tube seats. Remove the residual pressure valves and springs, if equipped. Remove the rubber cups from the ends of the pistons. On cast iron brake master cylinders, remove the O-ring or seal cup from the second land of the front piston. Clean the brake master cylinder with denatured alcohol or brake system solvent and blow it dry with compressed air. Do not, under any circumstances, use petroleum-based solvents to clean brake parts. Clean the cylinder bore with denatured alcohol or brake system solvent. inspect the bore for score marks and pits. Light scratches and corrosion on the cylinder bore walls can usually be removed with crocus cloth or a hone. However, deep scratches or score marks mean the cylinder should be replaced with anew one. If the pistons or bore are severely corroded, replace them. Always use new piston cups and seals when overhauling a brake master cylinder. All components should be assembled wet after dipping them in brake assembly lube.