Forum bmwbike.com

Mark,

I have just finished rebuilding my final drive according to spec. I decided to test the seals (all new) against oil leakage. I filled the drive with oil and turned it so that the crown splines were facing downward and let it sit there for about 5 minutes. To my surprise, oil had found its way past the seal. I wiped the oil off and set the casing still full of oil vertical but on a tilt towards the crown spline with the pinion facing up in a vice. Again to my surprise oil was not only passing through the seal at the crown spline end but also by the needle bearing seal of the crown and back through the space between the axle tube and inner core of crown wheel.Since I have new seals (which were properly seated and not damaged during reassembly) is this a common problem...or is it a problem? When the final drive is attached to the shaft on the bike, the oil level is such that it will clear the bottom of the larger seal. If the bike is tilted to the right however and left sitting, then the oil seepage will occur. There is a drain hole for the oil passing the larger seal so that it will not get to the brake surface but what about the other seal?
One comment I got is that the seals will leak if the shaft is not turning! Could you please give me more insight on this. I am ready to put the final drive in place but if you tell me I need to put in new seals again then I will do so.
If there is anybody out there that has experienced this "problem" please provide feedback.

Thanks,

Pierre Michaud

Forget it guys I solved my own problem with some enlightening feedback from Ed Korn.
The reason I was having seepage was because I
was testing the seals with the oil level over the contact between the
seal and shaft. Once installed the oil line never reaches this
contact.....even if you put oil right up to the brim of the filler hole.
As for the oil permeating between the axle tube and the core of the
crown gear and finding its way to the brake "chamber", this was residual
oil hypoid 90- that I had squirted inside the casing before I placed the
crown and fitted the cover.

So that little drain hole is there because the seal is not perfect.