1976 R90S Gearbox Rebuild - Drive Shaft Replacement

I'm currently rebuilding a 1976 BMW R90S gearbox for a customer. The original splines on the drive shaft (left side in picture) still has some life, but the customer wanted it replaced since his R90S is being restored. The drive shaft is still available from BMW, although with a hefty price tag. These 18mm drive shafts were used in airhead models from 1974 (/6 models) to 1980 (/7 models). I've replaced quite a few of these on restored bikes, it's time consuming, but I've learned a few tricks along the way.

From 1974 (/6 models) to 1980 (/7 models), this 18mm driveshaft was used in all airhead gearboxes. The left one is from the 1976 R90S gearbox and the right one is new.

From 1974 (/6 models) to 1980 (/7 models), this 18mm driveshaft was used in all airhead gearboxes. The left one is from the 1976 R90S gearbox and the right one is new.

When purchasing or rebuilding a used gearbox, the splines should be the first thing to check. New splines have an almost flat surface on the tip while old splines are sharp. My recommendation to the customer would be to re-use the old shaft if the bike is only a weekend rider around town and a brand new shaft if the bike will be seeing a lot of the road. Keep in mind at this point, the gearbox is gutted, so one should weigh the benefit of saving on labor now.

When purchasing or rebuilding a used gearbox, the splines should be the first thing to check. New splines have an almost flat surface on the tip while old splines are sharp. My recommendation to the customer would be to re-use the old shaft if the bike is only a weekend rider around town and a brand new shaft if the bike will be seeing a lot of the road. Keep in mind at this point, the gearbox is gutted, so one should weigh the benefit of saving on labor now.

After the groove bearing and bush is removed, there is a snap ring that requires compression to access, it's difficult. In the Clymers manual, they suggest using a steel pipe with a cutout window and a 12 ton press. I followed the Clymers method for sometime, but it was challenging. Here I'm using a cheap bearing puller from Harbor Freight, it compresses the shaft. This eliminates the press and steel pipe method. But regardless you should still have a 12-ton press for bearing jobs.

After the groove bearing and bush is removed, there is a snap ring that requires compression to access, it's difficult. In the Clymers manual, they suggest using a steel pipe with a cutout window and a 12 ton press. I followed the Clymers method for sometime, but it was challenging. Here I'm using a cheap bearing puller from Harbor Freight, it compresses the shaft. This eliminates the press and steel pipe method. But regardless you should still have a 12-ton press for bearing jobs.

Compressed and the snap ring is exposed. It's still a challenge sometimes to get that ring out. 

Compressed and the snap ring is exposed. It's still a challenge sometimes to get that ring out. 

After the snap ring is out, the shaft can be completely disassembled. The new parts include; drive shaft, Japanese made groove bearing, bearing cover plate, and cylindrical roller bearing.

After the snap ring is out, the shaft can be completely disassembled. The new parts include; drive shaft, Japanese made groove bearing, bearing cover plate, and cylindrical roller bearing.

Here is the completed drive shaft. 

Here is the completed drive shaft.