Oil leak from rear axle housing

[Robin]

Hello
I have a 1998 R1100S - cat removed, rechipped, Vanderlinde exhaust system. 45,000 miles from new. Reliable machine, good ride. Parked it in workshop in October, all OK. Ran it on stand for 7-8 minutes in November, all OK. In December noticed oil seeping from black cap on top of rear axle housing. Now Mid February and seepage continues - small oil slick under bike. Before I start on it, any views would be greatly appreciated.
Many thanks in advance.
Robin

[2Twins]

Hi Robin

You might like to investigate forward of the oil pool for anything obvious. My R1100S had an apparent leak when I got it, however, it turned out that the oil filter wasn’t tightened sufficiently. Another common leak point is the alloy washer on the oil cooler pipe.

There are plenty of YouTube videos if you have to address the main seal in the rear hub, but you may find it easier to eliminate other sources first. If you do have to replace the rear bearing seal, it seems to be good practice to check the bearing condition carefully.

You might also find this thread helpful ;

https://expeditionportal.com/forum/thre ... es.114500/

Good luck, and I’d be interested to hear how you get on.

Cheers
2Twins

[simon]

Hello Robin,
.. That's a breather cap, yes? Have changed the oil in back axle.. Maybe too much?
If not maybe gearbox output seal leaking, filling backend up somehow.. If you peel the back gaiter back is there oil there?
Is it oil or maybe brake fluid? Possible leak from caliper or maybe rear brake reservoir which is above-ish..
Here's hoping it's trivial

.. Edit: then I read the thread link... "what he said.." (hot fuzz )
If it is the gearbox seal, you can do it yourself if you're so inclined..

[Robin]

Thanks 2Twins and Simon - all very helpful suggestions. In fact a bashed-up knee has been preventing me tackling the matter but I hope to get down to it next week, better informed now with your helpful thoughts. Robin.

[Robin]

Final word - I drained the oil from the housing into a measured container. The amount that came out was 250ml. After a few hours to ensure that all the oil was indeed out, I replaced the drain plug and poured the oil back in. It filled exactly to the bottom edge of the filler opening. So the oil that had exited earlier via the breather was surplus to requirements i.e. overfill, as suggested. Took it for a 100 mile+ run and there is no sign of any repeat of the problem. (In mitigation I should add that this was the first time in the more than 20 years that I have owned the bike that I did not do the routine service myself!). Thanks again for the help.

[Humbug]

Good to see a resolution, especially when it is a painless outcome and a lesson to others to check the simple things first. Thanks for posting your findings.