Link to the original post:
https://blog.scottiesharpe.com/2013/03/bmw-2-swing-arm-leaks-final-drive-leaks.html?m=1
BMW /2 Swing arm leaks, final drive leaks
During a routine oil change, it was noted that the drive shaft housing was empty. Could it have been stolen by vagrants? A guy works hard for his oil just to have vagrants come and steal it.
Well, before contemplating a move to a safer neighborhood, BMW riders should remember that oil migration from the drive shaft housing to the rear drive is a common problem.
There are three ways that oil can migrate from the driveshaft housing to the final drive and they all have to do with the input gear on the final drive. This little guy:
Here are the three ways oil can get around this gear and into the final drive:
1. Through the seal.
2. Through the splines.
3. Through the threads which hold the collar in place.
The solution is to goop them up with non hardening sealant. Old timers used to use Hylomar. https://bmwclassicmotorcycles.com/index.php/catalogsearch/result/?q=hylomar
Some stores still stock Permatex.
When assembling the final drive input gear, clean parts thoroughly in solvent or carburetor cleaner.
Apply Hylomar or equiv. to the threads of the pinion gear bearing locking ring.
Apply a touch of grease to the seal surface of the coupling gear. Don’t put any Hylomar on the seal. It’s only for the splines and threads.
Next, apply Hylomar to the bottom of the splines on the coupling gear.
Install the gear and apply more Hylomar.
Install the locking ring (bent washer with positioning clip) and nut.
Failure to properly seal the splines and threads will allow oil to migrate from the swing arm into the final drive, over filling it. This is not a catastrophic situation, although it can lead to a leaky rear drive and oil-saturated rear brake shoes if the drain hole in the final drive is not clear.
If you do have a leaky pinion junction, you may notice that the fill plug of the final drive overflows when you remove it. To correct the situation, reduce the oil level in the Final Drive to just below the fill plug with a turkey baster and transfer this fluid to the prop shaft. If the fluid is contaminated, do not reuse it: rather empty prop shaft housing at swing arm drain plug and refill prop shaft with 150cc of 90wt gear oil. The manual says to use motor oil, but I suggest that you use something thicker if you want to live with this issue.