Borbin the 🐱

Driving around with my old BMW is fun, but I noticed oil spots (everywhere).
One of a common spots to leak oil is the transmission output shaft and this where mine was leaking too. The difference is that the leaking oil gets everywhere due to the rotating drive coupler disc.
The reason for the leak is that the surface for the seal is not perfect and this post is about to make it perfect.

First, a holder is made out of steel starting with a diameter of 16.3mm.

A rod is used as a lathe dog. Unfortunately mounting the shaft the other way around to hook into the jaws didn't worked.
Anyway, the shaft fitted exactly without any play.

The transmission output shaft is ready for machining:

I noticed that the existing surface was out of balance. Another reason why seals can fail over time. With several very light cuts, the surface is perfectly machined (MP4 or WMV).

Fine grit sandpaper is used to grind the surface to a smooth finish.

The new sealing surface of the transmission output shaft is finished and ready to use.

Update 06/04/2017:
Finished another one. Note the grooves that caused the leak!
Diameter was machined from 36.7mm to 36.55mm. We put it back in and drove around all day.
Perfectly sealed and no oil spill anymore using the same oil seal (48x36x8).

Update 06/22/2017:
And another one:

Update 04/30/2023:
Using 400 grit sandpaper is still too smooth for the sealing surface. See the Oil Seal post.