As many types and sizes of brake master cylinders were installed on the Chevelle, it may be wise to take all components to the auto parts store for proper fitting. Begin by removing the hydraulic lines at the brake master cylinder, collecting any fluid spillage with dry cloths, and plugging the ends of the hydraulic lines to prevent fluid loss or dirt from entering the system. For manual brakes, disconnect the push rod at the brake pedal inside the car. Unbolt and remove the brake master cylinder from the firewall or power booster, taking care to avoid dripping brake fluid on any painted surface, as it can ruin the finish. Drain all fluid from the brake master cylinder and place the unit in a vise, using wood blocks to cushion the jaws. For manual brakes, remove the push rod retaining ring, then take out the secondary stop bolt from the bottom of the front fluid reservoir (Delco Moraine) or from the base of the brake master cylinder body (Bendix). Remove the retaining ring from the groove and extract the primary piston assembly, followed by the secondary piston, spring, and retainer, which can be drawn out using a piece of bent stiff wire. Examine the inside surface of the brake master cylinder and the secondary piston for any scoring or 'bright' wear areas; if found, the entire brake master cylinder should be replaced. If the components are in good condition, wash them in clean hydraulic fluid, discard all rubber components and the primary piston, and purchase a rebuild kit containing all necessary parts for the overhaul. Inspect the tube seats in the brake master cylinder body where the fluid pipes connect; if damaged, replace them with new ones from the overhaul kit by threading a screw into the tube and prying outwards, then forcing the new ones into place using a spare brake line nut. Place the new secondary seals in the grooves of the secondary piston, assemble the primary seals and seal protector over the end of the secondary piston, and lubricate the cylinder bore and secondary piston with hydraulic fluid. Insert the spring retainer into the spring, then place the retainer and spring over the end of the secondary piston, ensuring the retainer locates inside the primary seal lips. With the brake master cylinder vertical, push the secondary piston into the bore to seat its spring, coat the seals of the primary piston with brake fluid, and fit it into the cylinder bore while holding it down to install the retaining ring in the cylinder groove. Continue to hold the piston down while installing the stop screw, then install the reservoir diaphragm into the reservoir cover plate, ensuring it is fully collapsed inside the recessed lid. Finally, install the brake master cylinder in the reverse order of removal, torque-tightening the attaching nuts to specifications, fill the brake master cylinder with fresh brake fluid, and bleed the brake master cylinder and complete hydraulic system.
