Before overhauling the Brake Master Cylinder, check the availability and cost of a new or factory rebuilt unit and a rebuild kit. The Brake Master Cylinder is mounted on the power brake booster. Remove as much fluid as possible from the reservoir using a syringe, and place rags under the fluid fittings while preparing caps or plastic bags to cover the ends of the lines after disconnection, taking care to avoid spilling brake fluid, which can damage paint. Loosen the tube nuts at the ends of the brake lines where they enter the Brake Master Cylinder using a flare nut wrench to prevent rounding off the flats on these nuts. Pull the brake lines slightly away from the Brake Master Cylinder and plug the ends to prevent contamination. Remove the Brake Master Cylinder mounting nuts to detach it from the power brake booster. Before attempting the overhaul, obtain the proper rebuild kit containing necessary replacement parts and any specific instructions. Inspect the reservoir or inlet grommet(s) for leakage, then remove the reservoir and grommets. Place the cylinder in a vise, use a punch or screwdriver to depress the primary piston, and remove the snap-ring, followed by the primary piston. Remove the stop bolt on the side of the Brake Master Cylinder and then the secondary piston, tapping the Brake Master Cylinder body against wood if the piston is stuck. Wash all parts in brake system cleaner, avoiding petroleum-based cleaners, and inspect the bore for deep scoring or damage that would require a new Brake Master Cylinder. Replace all parts included in the rebuild kit, lubricating them with clean brake fluid during assembly, and ensure all fittings and connections are tightened to the specified torque. Push the assembled components into the bore, coat the secondary piston with clean brake fluid, and install it, followed by the primary piston. Depress the pistons and install the new snap-ring, ensuring it is properly seated, then place a new washer on the stop bolt, depress the pistons again, and install the stop bolt securely. Install the new grommets and the reservoir, lubricating the grommets with clean brake fluid before pushing the Brake Master Cylinder onto the reservoir and securing it with the retaining screw. Before installing the new Brake Master Cylinder, it should be bench bled by mounting it in a vise and inserting threaded plugs into the brake line outlet holes, filling the reservoir with the recommended brake fluid. Remove one plug and push the piston assembly into the bore to expel air, replacing the plug before releasing pressure to prevent air from being drawn back in. Repeat until only brake fluid is expelled, then do the same for the other outlet hole, keeping the reservoir filled to avoid introducing air into the system. An alternative method involves covering the outlet hole with a finger instead of replacing the plug, allowing brake fluid to be drawn in before depressing the piston again. For installation, place the Brake Master Cylinder over the studs on the power brake booster and tighten the attaching nuts finger tight. Thread the brake line fittings into the Brake Master Cylinder, adjusting the position slightly if needed, and fully tighten the mounting nuts and brake fittings. Fill the Brake Master Cylinder reservoir with fluid, then bleed the Brake Master Cylinder and brake system if it has not been bench bled, having an assistant pump the brake pedal and hold it to the floor while loosening the fitting nut to allow air and fluid to escape, repeating until the fluid is clear of air bubbles, and test the operation of the brake system carefully before normal use.
Posted by HondaPartsNow Specialist 
