Vintage BMW Motorcycle Owners

Hi all,

I changed all the fluids in my 73 R75/5 this weekend. First time since I bought the bike.

I first did the engine oil and transmission. Nothing unusual there.

The next day I went to do the driveshaft. The bike was at room temp (75 degrees). I went to open the fill plug, as I started to remove it, fluid started flowing out! I put it back in and undid the drain plug. 350 ml came out!

I had previously checked the final drive, it was at the correct level.

I’m a little perplexed. The obvious (to me) answer is the last person overfilled the driveshaft oil. But I’m not 100% sure.

Is there any other possibility? Could the excess oil have possibly migrated from somewhere else? (Transmission or final drive?) or is that impossible?

Anyways, I drained it and filled with 140 ml.

It's probable not from the rear drive as the fluid would have to flow up hill to get into the drive shaft. Check the rubber boot between the gear box and the drive shaft. If it has a heavy coating of gear lube then you have a leaking transmission seal. I don't think you can change the seal without removing the gear box, because you need a gear puller (and usually a torch) to remove the drive flange. There is a calculation of how much leaking can you tolerate before fixing it. If it's not too bad keep riding it and check your gear box and drive shaft fluid daily.

Craig

Thanks.

I pulled the boot to check, and indeed some fluid dripped out.

However, I’m not sure that necessarily tells me the seal is leaking.

Because when I checked the transmission it was dead on at the proper level (yes, the seal could be leaking and the prior owner kept topping off the trans, however I’ve put around 400 miles on the bike and haven’t added any fluids).

Also, if someone really did fill the driveshaft to the top, wouldn’t we expect that some of that excess fluid would end up in the boot after miles of riding?

Yes, that is a possibility. Fill it to the proper level and check it every few days. If it stays level then don't worry about.
I thought you had checked it earlier and it had risen. Rereading your post I see that was the final drive you had checked.

Craig

I had a similar situation on my R75/5. It's been a couple years but as I recall oil actually came out the fill hole when I loosened it. I checked for tranny oil migration but found nothing. I ended up draining everything and filling to proper level. I checked the level before every ride for awhile and everything seems normal. I still don't know what happened.