R90S transmission intermediate shaft - FRU?

[Dave Backmarker]

After replacing the intermediate shaft with a New-Old-Stock RS transmission intermediate shaft, I then had to replace 1st, 2nd and 3rd speed gears to match this newer intermediate shaft. I found new gears from Bob's BMW. I also replaced all the bearings and seals and with new shims, I set the correct shim combination to match the shaft end-play specs. The transmission is now together and installed. This past weekend I was finally able to start up the R90S and try out my greatly refreshed transmission. Success! The transmissions shifts more smoothly than ever and now has a later design RS set of gears with stronger webs. And, as a bonus, I've learned a LOT about the insides of the airhead transmission. I should mention the great service from Bob's who offered to accept the very pricey gears back if I had miscalculated which gear I needed. Happily, I can still count the number of teeth on gears and the gear train fit together beautifully.

I do not recommend doing what I did if funds are tight. Rebuilding this transmission the way I did was very expensive. I'd suggest a good (smarter) path would be to purchase a used transmission and open it up to determine the wear on the gears then replace the bearings and seals. I've learned that we may swap many transmissions in our '70's airheads but there are approximately four different designs inside that prevent mixing parts from the early and later five speeds (e.g. the helix gears changed and the gear ratios changed over the late 1970's). Many parts from the early five speeds are no longer available which was what prompted me to purchase the RS intermediate shaft.

Thanks to all the posts here as well as the great video and parts from Cycleworks.net that made this big project for me a success.


DaveM
1975 R90S
2000 R1100RT

[lrz]

So that's what it looks like in there! Thanks for the photos / info & glad you worked it all out.