Back end oil leak

[Delpel]

Noticed some oil around the large rubber gaitor before the final drive unit. Upon further investigation I also noticed a small leak from the rubber gaitor at the gearbox. This leak leads me to believe the leak is at the gearbox end and running down the inside of the swinging arm. We are not talking lots of oil but enough to cause me some concern.

Questions then.

1, The manual says use approx 0.8l at oil changes. When I filled the gearbox up, the bike was on a paddock stand and I filled up to the bottom of the threads on the filler bung. Have I over filled it?

2, I have used Mobil HD oil of 85W-90A GL5 spec. The manual calls for 90W.

So where is the oil likely to be coming from and how big a job is it. Also when should I start getting stressed about this?

Cheers

[gus]

Hi derek
It does indeed sound like the gear box output seal has failed,if the gerabox oil is running down inside the paralever.If it is,then it can be replaced with the gearbox in situ.The manual says you need a special tool(puller BMW 00 8 590)to remove the seal.You may be able to use a hooked tool to get behind it and pop it out.Though i cant see how far recessed it is.You will need to remove the paralever arm to do the job,no big deal really.I,ve recently done a gearbox input seal on a friends S,not for the faint hearted as you have to remove the gearbox which involves removing the rear of the bike.C frame included!I didnt use any special tools as the seal could be prised out with a screw driver and a deep 24mm socket acted as a drift to get the new seal to seat.
Check the level when the bikes flat on the ground(both wheels).You may have overfilled it.You are correct in that the level should touch the bottom threads of the filler neck.
The oil your using is fine.My mates started leaking when he changed to synthetic oil(mobil).Its like water,so if a seal is iffy it will find a way past.
I would double check where the leak is from first,it could be coming from somewhere else.Check again to make sure.If it is gearbox oil it will stink!
I would come and do it for ya.But i dont think you paying my airfare and hotel bills would be cost effective!
all the best
gus

[bigblackfalco]

Del,sounds like gearbox output seal to me.Had one go myself.If you are intending to do the work yourself and you intend to hang on to the bike for a few years,do yourself a favour and instead of replacing with the same seal,take the old seal out and take to a bearing trader where hopefully you can get it matched with a double lipped seal.As it suggests,it has 2 lips which is twice as good at retaining the oil!
Job is pretty easy for anyone with a bit of common sense.
Bailey.

[gus]

Bailey
When i changed the gearbox input seal the new seal was different to the orignal.I suppose BMW keep looking for better alternatives too.
Good call on taking it to a bearing supplier to get a better alternative to the original.
Was the seal easy to get out without special extractors etc etc when you changed yours?
gus

[bigblackfalco]

Bailey
When i changed the gearbox input seal the new seal was different to the orignal.I suppose BMW keep looking for better alternatives too.
Good call on taking it to a bearing supplier to get a better alternative to the original.
Was the seal easy to get out without special extractors etc etc when you changed yours?
gus

Yes I used a special tool:READ: big screw driver
BMW have had this strange theory over the years that a single lipped seal damages the output/input shaft surfaces less than a double lipped.
The truth is that a double lipped seal very rarely fails in the complete service life of the bike.
It's the old thing "if it aint broke,don't fix it"!
Bailey.

[Cusi]

Del, take the money!

Regards Cusi