where is my driveshaft oil going?

[RSMike]

After just under 1K miles my driveshaft oil has dropped by close to 50%, It was at a similar level when I did a first oil change when I got the bike, I don't believe its leaking into the rear hub, here is what that looks like, i.e. all nice and dry:

So is it leaking forward and if so where would that mean it is going to?

[Bob_Roller]

Have you checked the oil level in the final drive ?

It's not uncommon to have the oil migrate from the drive shaft area into the final drive .

If the oil seal isn't the problem, the oil can get past the threads under the large nut that holds everything together in there .

There's a note in the BMW shop manual, that cautions you to put a thread sealant, or oil can migrate into the final drive from the drive shaft area .

[nhmaf]

+1 with Bob.   Put the bike on the centerstand on a flat surface.   slowly remove the fill/check bolt at the back of the final drive housing.   The oil level, if full should be just to the bottom threads and may slowly start to drizzle out.   If overfull from oil from the drive shaft, the oil will start to spurt out the plug until it drains down to the correct level.

[wirewrkr]

+1 with Bob.   Put the bike on the centerstand on a flat surface.   slowly remove the fill/check bolt at the back of the final drive housing.   The oil level, if full should be just to the bottom threads and may slowly start to drizzle out.   If overfull from oil from the drive shaft, the oil will start to spurt out the plug until it drains down to the correct level.

He has an 80 model with the old style final drive no level plug in the back.
The check on the early bikes is to have the fluid level at the bottom of the fill plug threads

[RSMike]

Yes, I checked the final drive ( which I also last filled at the same time as the drive shaft), final drive oil level was good, if anything a fraction below the bottom of the threads, so I actually added a very small amount there also.  :-/

The reason I checked the driveshaft today was I was leafing through the receipts given to me by the PO, some other PO obviously did a lot of work on the bike in 1995 and one of the items purchased was a 2nd hand driveshaft, this reminded me that the driveshaft oil had been low when I first got the bike, so its probable the bike did have driveshaft work done to it..............

[Dizerens5]

The oil can also pass forward into the gearbox (transmission). Surprising but it's happening on my 79. Not sure how to stop that easily. I just top up the shaft occasionally, mixing in some Greased Lightning gear additive and hoping that some will stick to the u.j. on its way past. So far so good.

[RSMike]

The oil can also pass forward into the gearbox (transmission). Surprising but it's happening on my 79. Not sure how to stop that easily. I just top up the shaft occasionally, mixing in some Greased Lightning gear additive and hoping that some will stick to the u.j. on its way past. So far so good.

Thanks, I think that is probably what is happening mine, as last time when I removed the gearbox filler the oil immediately poured out, and doing some searching now, I found this thread:
http://www.advrider.com/forums/showthread.php?t=29589

Which seems to indicate its not that uncommon to have the oil moving forward, and the that the 150cc filling guideline may be too much and sticking with 100 may be better, one poster in the thread above even suggested BMW may have at some point issued a bulletin revising the fill amount to 120cc.

[Semper Gumby]

Hi RSMike.

If you put the book quantity (150cc) in the drive shaft and drive fast enough (over about 65mph) the oil can get slung through a vent hole into the transmission.  

You can confirm this by opening the tranny fill hole on the LH side and seeing if any excess issues forth.

This can be mitgated somewhat by filling the drive shaft with only 100-120cc of oil.  Airhead guru Oak says the drive shaft will run safely on even less than that.

[RSMike]

Hi RSMike.

If you put the book quantity (150cc) in the drive shaft and drive fast enough (over about 65mph) the oil can get slung through a vent hole into the transmission.  

You can confirm this by opening the tranny fill hole on the LH side and seeing if any excess issues forth.

This can be mitgated somewhat by filling the drive shaft with only 100-120cc of oil.  Airhead guru Oak says the drive shaft will run safely on even less than that.

Thanks, Bill, its all becoming clearer now, I am known to push the old girl along at 70ish,  [smiley=thumbsup.gif]
I must pull the tranny oil fill to confirm, and let the excess out

OK, I have pulled the tranny fill plug, and exactly the amount of oil that was missing from the driveshaft ( about 60cc) poured out. Of course since I refilled the driveshaft , I'm probably going to need to do that again after another while, and that usual funky tranny oil smell now pervades the Garage   [smiley=huh.gif]

So meanwhile I have devised a dipstick for the driveshaft, its just a large tie wrap pointy end, bendy enough to push down around the shaft to get an indication of how much oil is in there.