After some advice. Just stripped my 1986 calipers to refurb and the pistons are good at the top but at the base theres some moderate corrosion. Tried cleaning it off with a soft wire brush in a dremel and it feels smooth but wont clean off. As its the part below the seal and shouldnt pump any were near, will the pistons be ok or should they be replaced. Cheers Ogri
Look at it under a magnifying glass--If it's just a stain or discolored aluminum probably okay, if the surface is pitted then might leak.
Classic example of not changing brake fluid every few years If the area of the piston will not get to the seals (both dust and piston), just clean it as best you can with steel wool and put it together. Change brake fluid in a year or so after caliper rebuild, as new fluid will become contaminated in about a year. After that, change fluid every few years to prevent similar corrosion in the brake lines/calipers.
Thanks for the responses. The bike had been sat for years before I got my hands the fluid has almost turned to dry glue like substance not even brake solvent is shifting it. I think i will be replacing the brake lines as well who knows how much gunk is stuck there.
