Leaky seal on rear drive? K1100LT

[Kevin1100]

This is the first bike I have (and have worked on). I have quite a bit of experience working on old cars but on this bike I'm still trying to find out what is what exactly. When taking the rear wheel off I noticed the wheel bolts were wet with fresh oil (I have replaced the final drive oil recently). At that point I wasn't sure if that was a problem or maybe that's normal on these bikes, but then I found a lot of greasy old oil on the brake disc as well. I have added a picture on which you can see black sooty grease behind the ABS ring and also in the brake disc vent holes. It's no big leak because there's no dripping or anything but an oily brake disc is not something I see as a wortwhile mod to this bike. I've been looking online a bit but can't find exactly what my problem might be. It's probably just a seal behind the brake disc but I was wondering if you all might be able to give me some pointers in the right direction, for example what the name of the seal would be. The PO kindly gave me his BMW service manual too which I have found helpful up until this point. It's great if you know what you are looking for, less great if you are grasping.

Thanks in advance!

[Scott_]

https://shop.maxbmw.com/fiche/DiagramsMain.aspx?vid=51711&rnd=10232024

part #1.

[Laitch]

https://shop.maxbmw.com/fiche/DiagramsMain.aspx?vid=51711&rnd=10232024
part #1.

[Kevin1100]

That's awesome guys, thanks both. Looks to be a pretty simple job, or am I mistaken? From what I can gather it's a question of removing the brake disc and the crown wheel housing cover and it'd be the first thing I see. The manual says to heat the housing cover to 100 degrees C, is that really necessary? And is this job doable while keeping the bearings in place or would I need new bearings as well? They seem quite costly and mine are in good order still as far as I can tell.

[Laitch]

The manual says to heat the housing cover to 100 degrees C, is that really necessary?

Somebody else might be able to put that manual to good use if you don't intend to believe it. Post it for sale for at no cost to anybody who is interested in it on eBay.nl. Consider that as your good deed for this month.

[Kevin1100]

Haha that's fair, it's actually a pdf copy I'm more than happy to share with anybody who would like one too. I will rephrase my question. I have never seen the need to heat components on the cars I've worked on in the past. Since from the diagram it seems that it's parts bolted together, what does the heating do?

[Laitch]

Just follow the instructions. Some components in both autos and motos are heated either to release, or fit, by expansion. Bricks are no exception. Also, in Bricks BMW occasionally used a type of Loctite on some fasteners that must be heated so the fastener can be unscrewed. Ignore all this and you'll likely be spending more time than usual with screw extractors, drills and torches.

You and Toto aren't in Kansas anymore.

[Ingo]

I've never had that particular area apart, but nonetheless follow the manual.  There are plenty of parts that need heat and/or freezing for removal/install. For example steering bearings, certain housing covers like on the old boxer's gear box... This also applies to cars...

[Kevin1100]

Today I replaced the crown gear seal. All in all a super easy job, I was able to just pry it out with a flathead without taking the whole housing apart, just taking the brake disc off. I let the bike run for a few minutes with the wheel and brake disc off to see if the leak was fixed. I noticed some oil weeping from the lug bolt holes when I shut the bike off. The lug bolts were always drenched in oil, that's how I discovered this leak in the first place. But now I'm not sure if that oil I saw is residual oil I didn't get out or if another component in the final drive could be leaking?

I checked my transmission oil and using the same dipstick I used to fill it 1000km/3 months ago, it still 100% the same as when I filled it up, so it doesn't seem that transmission fluid is leaking into or towards the final drive.

I may be jumping the gun here but if there are other symptoms I could look out for I would be glad to know them so I can keep an eye on it. For now I've thoroughly cleaned the bolt holes again and hope that any residual oil will go away after a few rides and the leak is finished.



All in all an interesting day. Came to replace the crown gear seal, was done with that in less than 30 min, then spent a good while replacing the glazed brake pads for new Brembo's (rear brake pedal finally feels firm now too) and then suddenly my starter motor wouldn't stop running. Figured the relay would be welded for some reason but my battery wasn't anywhere near low or old. Checked the relay anyway but it seemed to be in great condition. Put it back and the problem was fixed. No one can tell me there's not a decent bit of black magic involved with these bikes. I guess the contacts were just stuck together for a bit for some reason. I'll be riding with a 10mm socket in my jacket from now on to disconnect the battery if needed.