Final drive oil seal

[jamestnewsonr65]

The last couple of times I've been out on the bike I've seen a thin strip of oil around the coupling of the rear wheel to the final drive unit. Also some oil on the outside of the wheel as it has been rotating.

Thought I better have a look and see what was going on, and found a coating of oil all over the inner brake surface. I wondered why my rear brakes were ineffective ha!

I suspect it's the oil seal as I could see oil at the bottom of this under the ring gear , where the bike had been sitting for a few days.

Looking at he clymer manual it looks like I need a new gasket and oil seal. Is it just a case of removing the gear cover (with a bit of heat) and replacing the oil seal and gasket, then reassembling. I can't work out from clymer if it goes further than this. I suspect not.

Thanks.

[jamestnewsonr65]

Just having a look on the motobins site and seems there are a few final drive seals.

I assume it is the output seal (2nd in the list) on this page that I need along with a gasket for both ends.
https://www.motobins.co.uk/mobile/bmw-parts3.php?bikeref=&P=1&model=R%20Series%202%20valve%20Twin&M1=15&M2=1930

[Tony Smith]

Just having a look on the motobins site and seems there are a few final drive seals.

/quote]

Ok, there is one behind the coupler (the thing that you see if you take the final drive off), you need expensive special tools to get to this one, hence it is nearly almost declared "OK" by home mechanics and shops that do not have the tooling. They are actually pretty safe (mostly) leaving this one as its main job is top prevent migration of oil from the shaft housing (swing arm) to the final drive - a generous coating of thick wheel-bearing grease in the coupler will pretty much do the job on its own. Have said that, after 30 year it probably should be replaced.

Next is the big expensive one, to get to it you (obviously) need to undo all the bolts that secure the inner cover of the final drive, but what isn't obvious is how to remove it. Many manuals omit this, you use a pair of 5mm bolts to press the cover off the housing. Take care with the shims, particularly on reassembly and when fitting the new seal a crankshaft seal fitting dolly is a big help as is a can of whatever your favorite alcohol that comes in an aluminium can (you use this to protect your brand new seal from the drive splines, although soothing the nerves is equally valid.

Lastly there is a seal hidden in the other (outer) side of the final drive - depending on the mode of your final drive this can be a pain to get to casing - all I can say is that the one that is there is 30 years old - replace it.

Oh, and whilst you have your final drive strewn from one and of your workbench to the other, how are the drive spines? And for that matter, the bearings? The bearings do run in oil in a sealed environment so if it s kept clean and water free chances are they will outlive you, but it is worth while to have a look and feel. Mine felt fine, but for some reason the inner cage in the big expensive one (it had to be that one didn't it - sod's law) was breaking up, so I replaced it.

[montmil]

Prior to committing to remove the Cardan cover and replace the large oil seal, do check the rear brake camshaft and the condition of the small o-rings - usually two- that are supposed to seal the final drive oil reservoir from the interior of the brake drum.

Mere pennies to purchase, the o-rings are BMW's revised design to have owners buy more rear brake shoes.

[mrclubike]

The cover gasket is a job to clean off

The  seal behind the crown gear isnt to bad to change
just heat the housing up with a heat gun and the bearing slides out  
Then replace the seal and reheat the housing and reinstall bearing.

[davidpdx]

I had the same problem and did what Monte suggests which cleared up the problem and it had not returned in the last two years. Never did quite get my head around how it works but a win is a win however you get it. Cheap and pretty easy to try and you aren't out much if it doesn't work.  

[jamestnewsonr65]

Thanks for the replies.

I've already replaced the small o rings on the brake camshaft when it was rebuilt a year ago so they are all fine.

I could see oil collected around the seal around the splines so suspect it is this. I've ordered the gasket and seal set from motobins so hopefully will get it sorted in the next couple of days.

Happy to dive into the bevel drive to change the 1st oil seal but not sure I have the skill with the others.

[montmil]

Thanks for the replies...mHappy to dive into the bevel drive to change the 1st oil seal but not sure I have the skill with the others.

It's actually a fairly simple procedure, James. Sing out when your parts arrive and we'll walk you through it.

[jamestnewsonr65]

Parts were delivered today. I oredered the full gasket and seal kit so it comes with camshaft o rings, replacement felt washer etc.

Took the bevel drive off the bike today and plan on diving in to it tomorrow. Splines all look OK as the bike had only done 17k miles when I bought it and had a good service history. Think the bike is probably still under 20k miles.

The oil in the drive shaft seemed a little dark and the drain bolt had a little black sludge on it. No metal just sludge.

If I get stuck I'll yell for help.

[Terry]

You  should check the thickness of the old and  new cover gasket. Your new one may be thinner. If so the side load on the large crown wheel bearing could be increased causing it to fail. There should be no side load on he large bearing and zero clearance is the recorded gap.
My new gasket was 0.04 mm thinner and it reduced the clearance between the cover and the bearing to the point that I could not turn the pinion unless I put on a socket and bar. Check the feel of the pinion first to see how easy it turns to get an idea of the now 30 years of preload, backlash etc.  you could get lucky.

[Terry]

You  should check the thickness of the old and  new cover gasket. Your new one may be thinner. If so the side load on the large crown wheel bearing could be increased causing it to fail. There should be no side load on he large bearing and zero clearance is the recorded gap.
My new gasket was 0.04 mm thinner and it reduced the clearance between the cover and the bearing to the point that I could not turn the pinion unless I put on a socket and bar. Check the feel of the pinion first to see how easy it turns to get an idea of the now 30 years of preload, backlash etc.  you could get lucky.

[Tony Smith]

The cover gasket is a job to clean off

I didn't mention that fun little job, it's best if it comes as a surprise I reckon. Getting that gasket off took nearly as long as the rest of the job

[jamestnewsonr65]

So today I took the final drive apart and it was actually pretty simple. The drive and splines were all really clean and not worn at all which was good to see.

That gasket is a real pain in the butt, but it cleans up pretty well. I only replaced the oil seal around the splines as I'm pretty sure that is where the leak was coming from. The old oil seal was a bit thinner than the replacement.