GMC 18047594 Cylinder Asm,Brake Master

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To remove the brake master cylinder, start by placing rags under the brake line fittings and preparing caps or plastic bags to cover the ends of the lines once they are disconnected. Then, use a flare-nut wrench to loosen the tube nuts at the ends of the brake lines where they enter the brake master cylinder. Pull the brake lines away slightly and plug the ends to prevent contamination. Remove the mounting nuts and disconnect the pushrod from the brake pedal. Move the bracket retaining the combination valve forward slightly and remove the brake master cylinder from the vehicle. Remove the reservoir covers and diaphragms, and discard any remaining fluid. Mount the brake master cylinder in a vise with blocks of wood to prevent damage. Remove the primary piston lock-ring and assembly, followed by the secondary piston assembly. Pry the reservoir from the cylinder body and remove the grommets. Do not attempt to remove the quick take-up valve. To overhaul the brake master cylinder, inspect the cylinder bore for corrosion and damage. If any is found, replace the brake master cylinder body. Lubricate and press the new reservoir grommets into the body, then press the brake master cylinder body onto the reservoir. Remove the old seals from the secondary piston assembly and install the new seals with the lips facing away from each other. Attach the spring retainer and lubricate the cylinder bore. Install the spring and secondary piston assembly, followed by the primary piston assembly and lock-ring. Inspect the reservoir cover and diaphragm, replacing any damaged parts. Insert threaded plugs into the cylinder outlet holes and fill the reservoirs with brake fluid. Loosen one plug at a time and push the piston assembly into the bore to force air out. Stroke the piston multiple times for each outlet to ensure all air is expelled. Refill the reservoirs and install the diaphragm and cover assembly. To install the brake master cylinder, reverse the removal steps and bleed the brakes.

Start by placing rags under the brake line fittings and preparing caps or plastic bags to cover the ends of the lines once they are disconnected.