When maintaining wheel cylinders, take into consideration that they may need to be overhauled due to leakage or sticky operation. It's easier with new cylinders. Take off the brake drum as well as shoes, unscrew the brake line fitting, and remove the bolts securing the cylinder. Disassemble cylinder and replace rubber components; inspect pistons and bore, clean with brake cleaner, and reassemble with new parts. Install the cylinder again, attach the brake line, bleed the brakes then test before driving.