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tunnelrider
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New swing arm/ final drive gasket
10/12/18 at 06:28:55
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Hi everyone,

Symptom is a weeping swing arm / final drive join. It's not coming from the drain plug or filler plug.
Should I use gasket sealant when I replace this gasket? I ask this because some BMW gaskets don't require any sealant. The new gasket is from Motobins.
If there's likely to be another reason for the weeping please ignore my naivety.
Thanks in advance for any information.
  

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 1985 Black R65  -  1983 Ducati Pantah 500 - 2001 DRZ400 dirt only
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georgesgiralt
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Re: New swing arm/ final drive gasket
Reply #1 - 10/12/18 at 12:30:45
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Hello,
I've dismantled this part of the bile in order to powder coat the whole swing arm (and frame..).
The final drive had been put back with the plain paper gasket without anything and no leaks.
I used the proper torque to assemble the drive.
Hope this helps.
  
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Tony Smith
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Re: New swing arm/ final drive gasket
Reply #2 - 10/12/18 at 16:30:12
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BMW Engineers would have coniptions at the idea of you putting sealant on that gasket.

The reason is that the crushed thickness of that gasket has been carefully calculated so that the correct dimensions of the swing arm are maintained and the rear axle is true relative to the frame of the bike.

Or at least this is how it was explained to me by a now departed guru of all things BMW.

The reality is that this is another case of BMW stressing out to ensure a solution to a non problem. i would happily use a thin smear of a non-hardening jointing compound such as Hylomar and be confident the wheel alignment would not be affected.

BUT, if you clean the joint faces and use a new gasket, and then tighten the bolts to the correct torque, you don't need jointing compound.
  

1978 R100RS| 1984 R65 | 1984 XT350 | 1992 KLE500 | 2002 R1150GSA
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Mrclubike
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Re: New swing arm/ final drive gasket
Reply #3 - 10/12/18 at 18:42:54
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just make sure the axle is installed and snugged up be for you tighten the 4 bolts 
to make sure the axle bores are in line when you tighten the 4 bolts
Yes use some gasket sealer sparingly and use the gasket 
« Last Edit: 12/02/18 at 11:17:20 by Mrclubike »  

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tunnelrider
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Re: New swing arm/ final drive gasket
Reply #4 - 10/15/18 at 05:44:19
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Interesting job. Has posed more questions for me than the one answer for the leak, about how the whole swing arm and final drive set up works, considering the amount of abuse it gets. It was leaking from a sharp edge on the final drive face wearing through the gasket, not sure how that got there. Kinda looked like it'd copped a sharp stone from the side at the join (could be me), or a screw driver to pry open from the side (def not me). First thing -

On the twinshock final drive shock mount, what should be protecting the final drive housing from the shock absorber? A washer of some sort? Mine's got nothing currently.

Not sure if the Motobins gasket is as thick at the paper gasket on there before.

- This could lead to a new wear pattern on the coupling splines, not the end of the world as they have a lot of life left. On taking the diff off, the shaft/ rear drive coupling splines were wet with oil and otherwise clean. Black mark in the middle of the swing arm female splines from the drive splines.
Clymer says lube the splines on reinstall so I dutifully lubed the splines on the swing arm and drive couplings with high moly but wonder how long that stays on for considering the area is full of gear oil, does it get hot and it all goes out in the next oil change?
  

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Justin B.
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Re: New swing arm/ final drive gasket
Reply #5 - 10/18/18 at 14:01:41
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Not sure what has happened here but something got screwed up after this post.  Some sort of date stamp didn't match up in a quote, or something.  I couldn't really figure out what was causing this so I just deleted the replies starting where the error occurred.

Sorry...
  

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tunnelrider
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Re: New swing arm/ final drive gasket
Reply #6 - 12/01/18 at 21:56:42
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Hi everyone, just resurrecting this topic to ask a couple of things - I think I managed to see in the error message before that a thin washer sits between the rear drive and shock absorber on the shock mount?

Also would anyone know how long high % Moly paste would stay on the drive shaft/rear drive coupling splines in the presence of the swing arm oil? I followed the Clymer instructions putting that on but now wonder if it would turn into a nice grinding oil mix for any bearings the swing arm oil might lube?

Cheers in advance for any info.
  

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Mrclubike
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Re: New swing arm/ final drive gasket
Reply #7 - 12/02/18 at 11:09:21
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If you wheel drive splines are getting gear oil on them
(the splines between the wheel and final drive)
Unfortunately you need to repair the gear oil leak
It may be just the outer seal
But being that the splines are full of oil more than likely it is the inner seal
It isn't a really difficult job if you heat the housing up with a heat gun
The bushing #1 and bearing #3  will fall out 
Then you can change the seal  #2
Heat the housing back up and reinstall the bushing and bearing
(You do have a heat gun don't you every air head owner has a heat gun Wink)
of course the final drive really needs to come back off

The part that will make you curse is removing the gasket from the housing  Angry
« Last Edit: 12/03/18 at 20:53:09 by Mrclubike »  

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Mrclubike
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Re: New swing arm/ final drive gasket
Reply #8 - 12/02/18 at 11:14:32
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As far as spline lube normally you just clean and lube it every tire change
about 7000 miles or 11000 km
also replacing the O'ring on the brake shaft is a good idea
I use a quad ring instead of the O'ring
They last a lot longer  Cool
  

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tunnelrider
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Re: New swing arm/ final drive gasket
Reply #9 - 12/02/18 at 21:49:25
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Mrclubike wrote on 12/02/18 at 11:09:21:
(You do have a heat gun don't you every air head owner has a heat gun Wink)
of course the final drive really needs to come back off

The part that will make you curse is removing the gasket from the housing  Angry


Smiley of course I've got a heat gun and used it many times since! Thanks for the reply and diagram Mrclubike, sorry for my misleading post as I've already repaired the weep, it was just a matter of replacing the ripped paper gasket and smoothing out the nick that caused it.

Yep that gasket  Angry I had to go through the tunnel to buy a spray can of gasket remover, not cheap that stuff, cost $35! By then of course I'd already spent an hour getting half of it off but the spray worked a treat and it only took another 30min to get the rest of it off, including the PIA areas by the studs. Still got 3/4 of the spray left.
It looks from the diagram the inner seal #2 you have highlighted would stop swing arm oil from contaminating the large final drive bearing. Is that the seal that holds the swing arm oil from entering the final drive? 
Thanks
  

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Tony Smith
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Re: New swing arm/ final drive gasket
Reply #10 - 12/03/18 at 01:28:33
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The two seals arrowed respectively keep oil from the final drive housing from contaminating the outside world and your brakes.

If oil is getting into your final drive housing from the swingarm you have a different problem, and one that can be a bit expensive to fix. When you take the final drive off the bike there is a coupler that transmits drive from the driveshaft to the final drive - the "concave" part of the coupler is in the swingarm and the "convex" part sticks out of the front of the final drive and looks a bit like a gear.

If oil is getting past the seal in the nose of the final drive there are two choices - a "bodge' that actually works, or do the job properly.

The bodge consists of stuffing as much heavy axle grease as you can into the swingarm side of the coupler - don't be bashful get as much as you can in there. The grease will prevent, or at least greatly delay the migration of oil from the shaft to the final drive - this bodge has been working for around 15 years on the wife's R65/80 and stood up to a trip from here to Darwin and back. Best of all if the bodge fails and oil starts migrating again, for the price of one gasket and some grease you can simply do it again.

Fixing it properly is not a difficult job but requires special tools. You need a means of locking the ring gear in the final drive. The first one of these I did, I simply fed a piece of rag into the crown and pinon gears till they jammed and then removed the nut securing the input side of the coupler with an impact wrench.

Please do not do this as you run a good risk of blowing the pinon shaft out of its lower bearing mount - congratulations, you just bought a new final drive if you do that.

Next you need the special tool to remove the bearing and seal carrier - this was covered recently in a discussion in another thread and someone said they had bought an off-the-shelf driver a lot cheaper than even the imitation special tools made by Cycleworks  LLC.

Here are some pictures of the tools needed.

if you do this job, give the age of even the youngest twin shock R65 I would change ALL the bearings, which means you have a further expense of buying a pack of shims for setting the crown/pinon mesh (big hint, buy the same brand bearings as came out and you mostly need only minor shim changes if in fact any at all.

The little bearing that carries the rear of the pinion shaft is a known "bear" to remove sometimes, in fact sometimes the only way it can be removed is by spark erosion - take money.

Done right you are rewarded with a final drive that should run trouble free for at least another 35 years or more.
  

1978 R100RS| 1984 R65 | 1984 XT350 | 1992 KLE500 | 2002 R1150GSA
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tunnelrider
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Re: New swing arm/ final drive gasket
Reply #11 - 12/03/18 at 04:00:54
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Thanks Tony for the wonderfully detailed know how, hopefully I never have to look further into the rear drive.  Grin  If I do I now know where to look first Wink....  I'm lucky enough to report that every time I've replaced my swing arm oil there's been the same amount in there as I put in. My questions are simply based on how far the swing arm oil travels and whether lubing the drive shaft female/ rear diff male coupling splines with moly paste might damage any bearings. I find it hard to believe the moly paste would stay on the splines for long... But I'm just guessing sorry, have no research into the matter available.
  

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Tony Smith
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Re: New swing arm/ final drive gasket
Reply #12 - 12/03/18 at 04:16:37
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Moly paste goes on the gearbox input splines.

Heavy axle grease goes on the rear wheel drive dogs
  

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tunnelrider
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Re: New swing arm/ final drive gasket
Reply #13 - 12/03/18 at 04:33:51
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Tony Smith wrote on 12/03/18 at 04:16:37:
Heavy axle grease goes on the rear wheel drive dogs
                   


Sorry Tony, just need a bit of clarifying - by rear wheel drive dogs you mean the coupling I just replaced the gasket on?  S**t I better change the oil a couple times then. My bad.
Cheers
  

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Tony Smith
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Re: New swing arm/ final drive gasket
Reply #14 - 12/03/18 at 13:51:40
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Yes, grease goes in there. There isn''t enough Starbraughs  in the world!
  

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