BMW R850R Front Brake Master Cylinder Rebuild
This isn't a step by step master cylinder rebuild. You'll want a shop manual for that. These photos are hopefully intersting if you are doing a rebuild, or trying to figure out if it is time to rebuild.
This is the front brake master cylinder of the BMW R850R (probably identical to the R1100).
With the cover, boot, and brake lever removed, you can see corrosion around the master cylinder piston. This has been leaking for a long time, and is long over due for a rebuild. I should have peeked up under here long ago. There should not be brake fluid in the dust cover. This wasn't a "leak" per se, but things were long past needing a repair.
The piston won't come out until you remove the retaining screw on the side of the master cylinder.
Carefully cover everything (especially painted surfaces like the tank and engine cylinder) below and around the master cylinder. Brake fluid is very corrosive to paint, and I'm pretty sure it's a carcinogen.
