Sticking Frt Brake Caliper

[43248]

I'm bringing a '90 R100 GS PD out of retirement and the front brake caliper was totally stuck. Tapped on it a bunch, which freed it up some. Bled the brake but it still seems stuck in one quadrant of it's rotation. The brake fluid was real brown so it had absorbed quite a bit of moisture. I would appreciate any recommendation on how to proceed. Chiltons says that the seals have to be replaced if I tear it open to look for rust. The parts websites say that removing the pistons is a dealer only job but I guess they'll sell you the parts in case you want to tackle it. Thanks for any insight you might have to offer.

Dave

[squiffynimrod]

Your brake caliper appears to be similar to the ones I just rebuilt on the RT, but the part # of the kit is different from mine.
http://www.realoem.com/bmw/showparts.do?model=0479&mospid=47917&btnr=34_0631&hg=34&fg=05
The same listing from the RT has no mention of "ONLY FOR REPAIR AT THE DEALER'S"
The rebuild was really simple on mine, hardest part was getting the bolts holding the 2 halves apart (hint from the boards- leave the caliper mounted to the fork, break the halves loose then remove from the fork- way easier).
Not much help, but info.

[shire2000]

Splitting the caliper is the easy part, getting the pistons out, well that can be a problem. When you find the brake fluid is very brown, that not only means that it is contaminated. Expect there to be rust inside. Expect the little holes in the calipers to have gunk stuck in them. Pray like heck that none of the little holes are plugged up solid. It can all be fixed, just depends on how much you want to spend.

I have had some that were so bad that I would pull it apart as far as it would go, getting dust seals off and breaking the pistons apart. Remove the bleeder screw ( usually totally plugged) and drop the 2 halves into a pan of solvent for a day or two. Take it out every few hours and work on getting the pistons moving, drop it back in the solvent. Eventually they come apart and I can clean them up to see if there is any major damage. If not looking to bad, finish the cleanup and replace every seal and usually the pistons (but not always). Reassemble using good clean brake fluid as the lubricant to slide the pistons back in. Replace any "O" rings between the halves and bolt it up. Replace the bleeder screw with a new one and bleed it well. Take the bike for a very short spin and bleed it again.

I also find that if a bike has been sitting long enough for this all to happen that I usually replace the brake lines at this point as well and may rebuild the master cylinder. That way I know that everything is working as it should. I never skimp on brakes, it just isn't worth taking the chance.

:ca