The piston before and after cleaning, as the piston was already in good condition it was cleaned with a soft Scotchbrite pad to remove the stubborn marks and washed down in brake fluid. If your piston is corroded you can clean it up with a few long strips of fine grit wet & dry paper, finishing with something like 1000 grit. If badly pitted the piston should be renewed.

 

The caliper body was oxide blasted before being stripped down, and the light rust marks were cleaned off again with a Scotchbrite pad. The whole body was then washed in a solvent (brake cleaner is fine) to remove all traces of dirt. If the body is badly pitted you may have to use wet & dry as before on the piston. Again, if the caliper wall is badly pitted you should throw it away.

Be sure to scrape out any dirt in the groves which the seals locate, unless these are completely clean you will find it is impossible to fit the seals, this is especially true of the piston dust seal.