Boxerworks.com

Hello,
Newbie here. I have a '76 R90/6 that I let sit too long without riding (garaged). Checking fluids now in preparation for getting the bike back on the road, found an "abundance" of oil in the rear drive. Can someone direct me to the best discussion regarding a diagnosis and fix? Many thanks.

Sure thang. Scroll down towards the bottom of this page. Welcome to by the way!
http://www.w6rec.com/duane/bmw/finaldrive/index.htm

I had that problem when I first got mine. Obviously it's migrating from the drive shaft so all I did was to reduce the amount of oil I put in the drive shaft from the official 150CC to the widely recommended 100 - 120CC and the problem has never happened again since. I suppose the fact that mine had also had been stood for a couple of years and is now in regular use might also be a factor.

This can also happen with correct oil levels in both the final drive, swinging arm and gearbox; but without one critical original part: the hollow screw that secures the speedo cable (and battery earth lead) to the gearbox. When I had got my recently acquired /5 home, the rear tyre was covered in gear oil, which had leaked out of the top vent hole in the FD because the previous owner had used a standard, not hollow screw for the speedo cable. This caused the air inside the gearbox to pressurize when the engine and gearbox warmed up, pushing gearbox oil back into the swinging arm, and from there again on into the final drive, until it got full and vented out the excess.

If I hadn't read about, and thus knew of the peculiarities of the gearbox, drive shaft and FD oils before, it would have taken me much longer to fix the problem; which was sorted by just replacing the speedo cable screw with one intended for the job.