I work for an automotive parts rebuilder, and one of the items we handle is brake calipers. We clean most of our calipers with heat. 750-800 deg. F. in an oven for about four hours. After that, they are steel shot blasted and dipped into a rust preventative that is compatible with brake fluid. That is beyond what the home mechanic could do.
If you have access to glass beading equipment, that is the best alternative. The calipers themselves can be de-greased with mineral spirits followed by a cleaning with some of that Brake-Clean stuff to get rid of any residue. If the calipers aren't that dirty, the Brake-Clean stuff might do the job of de-greasing. The glass beading will get into the all important bore area. Specifically the square O-ring groove and boot groove. The seal groove after cleaning should look smooth. Any obvious pits will cause problems. My past experience shows that these grooves hold up very well. The boot groove is thin, and all the crud must be removed, or it will be difficult to get the new boot in. Again, glass beading cleans this out real good. The bore itself is not an issue, as the square O-ring seals on the exterior of the piston. Just so long as the bore is clean. If there is any pitting on the pistons, they will have to be replaced. You cannot accept anything other then a perfect finish...that's where the seal seals.
Now for the threaded plug on the early calipers. There is an O-ring that seals it, and it is threaded in. When I did mine, I took out the plug, and just used an appropriate sized O-ring I got from work. Any EPDM O-ring that's the same size as what's in there will work. I would imagine, that there are a mess of those calipers out there that have been rebuilt a half a dozen times and never had that plug out. Besides, who has a screwdriver that big?? /bcforum/images/%%GRAEMLIN_URL%%/jester.gif
So, why is that plug there??? I thought about it for awhile and came to a conclusion that I feel is correct. Anybody have any thoughts on that??