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Old 10-07-2012, 03:47 AM   #1
ywouldi OP
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Eh? Leaky Bevel Box

Hi, new to this forum but recently bought a 1983 R80 as a little (but maybe a bit too big) project. It's generally in good condition and I intent to turn it into a street style scrambler thing.

Anyway, noticed some oil dripping down on to the tyre and it appears there is a slight leak from the bevel box, seems to be from the main box rather than from the shaft or something. Looking at Motorworks (I'm in the UK) there appear to be a couple of main seals:

Bevel box cover gasket ( 1981 on not Paralever ) | TRA11097
Bevel box to swingarm gasket ( 1970 on ) | TRA11098
Brake shoe cam O-ring 3 required ( 1981 on ) | BRA06328
Rear drum brake cam flat washer ( all models 1970-96 ) | BRA60107

Would this lot typically fix such a problem and is it something that a reasonably incompetent DIY mechanic could do? I have hear horror stories of the bevel box!

Thanks,
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Old 10-07-2012, 06:46 AM   #2
Rucksta
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Brake shoe cam O-ring 3 required ( 1981 on ) | BRA06328

Try this one first.
Common
Cheap
No special skills or tools required.
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Old 10-07-2012, 07:22 AM   #3
ywouldi OP
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Originally Posted by Rucksta View Post
Brake shoe cam O-ring 3 required ( 1981 on ) | BRA06328

Try this one first.
Common
Cheap
No special skills or tools required.
That sounds like a good idea. A Haynes manual is on it's way so I'm sure that will help and from the pictures I've seen online it should be fairly straight forward.

The oil does seem to be coming from between the casing and the hub but I suppose the brake cam o-ring on the inside could be the one that's let go.
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Old 10-16-2012, 02:39 PM   #4
ywouldi OP
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I bought all of the seals anyway as they were cheap and I want to try and get it all done in one go. I have searche for ages to find a guide to replacing the larger seals but cannot find anything at all. Does anyone have any useful information at all? The Haynes manual is useless in this regard as it simply says to send it to a BMW dealer. I thought that I wouldnt be touching the gears and so won't need to reshot etc.

Thanks

Ben
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Old 10-16-2012, 03:19 PM   #5
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Quote:
Originally Posted by ywouldi View Post
I bought all of the seals anyway as they were cheap and I want to try and get it all done in one go. I have searche for ages to find a guide to replacing the larger seals but cannot find anything at all. Does anyone have any useful information at all? The Haynes manual is useless in this regard as it simply says to send it to a BMW dealer. I thought that I wouldnt be touching the gears and so won't need to reshot etc.

Thanks

Ben
Found this now which seems useful, maybe it will be a bit too much but it does seem that the big gasket can be replaced without interfering with the complicated bits. Am I right?

http://www.advrider.com/forums/showp...4&postcount=45
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Old 10-16-2012, 06:08 PM   #6
disston
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There is a problem with a DIY mechanic of any level of experience doing a seal replacement on the final drives. There was a time we got the same gasket the units were built with and we did this. Now the gasket, #13 in the exploded diagram, is not the same material. It is a different thickness. This gasket will effect the position of the cover which will change the spacing for the large bearing pre-load. The final drive has to be reshimed after replacing the gasket and this is done to get at the seal. Failure to properly shim the bearing, notice #6 in the top drawing, that is a shim, will cause failure of the unit. In this case a final drive unit failure is not something that can be fixed. It means the unit can die.

Fine a dandy you think? But in order to do the shimming special tools are needed. I don't think you can even buy them. I've never seen a picture of what they look like.

The small seal on the pinion side may be doable by a home shop mechanic but you will need some other special tools. Just a couple of sockets I think.

Replace the O-ring seals in the brake cam hole and this will probably fix it. If not prepare to send it to somebody who can fix it.

You can probably return the parts for credit. There are plenty of other things to work on.
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Old 10-16-2012, 07:33 PM   #7
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I think I'd go along with Disston in just doing what's needed. This is why....

If the pinion:crown isn't well set, you may just get this eventually...




Whilst you have the wheel off, check the splines. If they're horribly worn and need replacing, then this is the time to get the whole lot done professionally, including seals and resetting the pinion:crown relationship.

Of course, if you have the skills and tools, then have a crack. If so, pictorial documentation would be great as it's an area that is seldom attempted and the internet resource to follow for others is generally lacking. You'd need a selection of shims and a few of the big gaskets for some trial and error testing I expect. I've read something about blue dye to check the interface b/w pinion and crown...
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Old 10-17-2012, 12:33 AM   #8
ywouldi OP
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Ahh, great, thanks both. Now I understand why I shouldn't touch it, I'll just do the brake cam o-rings then and see how it goes. I think it needs a new breather/filler cap as it has been painted which I gather ca cause it to over pressurise and force oil past the seals as well, although I don't think this happens in this case as it's not been ridden at all recently.
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Old 10-17-2012, 06:20 AM   #9
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Quote:
Originally Posted by ywouldi View Post
Ahh, great, thanks both. Now I understand why I shouldn't touch it, I'll just do the brake cam o-rings then and see how it goes. I think it needs a new breather/filler cap as it has been painted which I gather ca cause it to over pressurise and force oil past the seals as well, although I don't think this happens in this case as it's not been ridden at all recently.
You can test the breathing on the filler cap by blowing through it.

If its blocked the dome is a press fit on the riser.
You can remove the dome with a pair of pliers if you need access to clear a painted blockage.
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Rucksta screwed with this post 10-17-2012 at 08:22 AM
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Old 10-17-2012, 07:49 AM   #10
Airhead Wrangler
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Quote:
Originally Posted by disston View Post
Fine a dandy you think? But in order to do the shimming special tools are needed. I don't think you can even buy them. I've never seen a picture of what they look like.
I've never seen the factory tools either, but It's doable with a depth gauge and parallel bars. I've never done it myself though. Just changing out the outer shim for the BIG bearing isn't THAT tough. When you have to change out the brass shim under the tapered roller bearing or the pinion shims, that's when it gets tough. Anything with the potential to change the position of the crown and pinion in relation to each other is dangerous territory. Gotta bust out the Prussian blue marking dye to check gear engagement, etc. Reshimming the outer bearing won't do that though. Just gotta measure the depth right and accurately account for how much the gasket gets crushed and you're good. Surely not for a novice, but it's also not rocket science.
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Airhead Wrangler screwed with this post 10-17-2012 at 07:58 AM
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Old 10-17-2012, 10:54 AM   #11
Wirespokes
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If the new gaskets are that much different, an easier route would be to source the same thickness gasket material as original and make your own.
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