Will '83 R100CS rear drive fit '74 R90S? Easy?

[Jean]

And remember the final drive ratios must be the same or your speedo will be only decorative!

[Garnet]

And remember the final drive ratios must be the same or your speedo will be only decorative!

It's a BMW, I thought that's all the speedos where.

[Deleted User 287]

And remember the final drive ratios must be the same or your speedo will be only decorative!

It's a BMW, I thought that's all the speedos where.

Actually, with the proper mis-match of final drive ratio to speedometer ratio, you could probably get an accurate reading.

[p2squared]

Best I can tell from the vent thing on top of the final drive. I think.

Had just noticed the other day gear oily mess on right side of rear rim, tire
diff. Filler's and drain plugs on rear drive and drive shaft all tight and
been a while since I changed, and haven't topped off or checked
in a while.

Cleaned everything so's I can tell a bit easier where it's coming from
after a few miles, hopefully issue will be more evident as to what/where
coming from.

Thoughts as to what could be?

Thanks,

p2

[Deleted User 62]

It sounds like you are getting oil transfer from the drive shaft to the rear drive, causing it to overflow. Try this, drain the oil from the drive shaft and measure what you get. Then refill with the proper amount. I'm guessing you will find no oil in the drive shaft. If so, it's not that big of a deal to replace the seal between them, but it requires a couple special tools and mechanical skills. It may also be oil coming from the transmission, so check and see if the oil is level with the bottom of the threads while on the center stand. If it's not, then the seal on the transmission output shaft is probably leaking, too.

[Duane Ausherman]

It is much simpler to check for transfer. Just remove the fill plug on the final drive and see if oil comes out. If it comes out over the top, you know that it came from the swing arm.

It isn't a big deal to fix the transfer, but the oil has three paths and it is seldom the actual seal. Info on my site.