Cracked flange on final drive

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two wheel tango
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Cracked flange on final drive

Post by two wheel tango »

Going to be a while before I get her back on the road... need to figure out options to fix :(

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towerworker
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Re: Cracked flange on final drive

Post by towerworker »

Wow.......never seen that one before! Not that it matters now but how did it happen?

Unless you can find a really sharp welding/machine shop I think you're looking at replacement. BeemerBoneyard would be the first place I'd look. That attachment point of course is pretty important. I would like to see CycleRob offer his take. I bet some folks would say "try some JB Weld!"

Come to think of it........I wonder if any type of weld repair might be out of the question because of possible deformation of the unit. I just don't know.
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Re: Cracked flange on final drive

Post by trickytree »

My guess....hammering the pad pin out? Must have been well seized in!
Could probably be welded but I wouldn't, just fit a replacement plate.
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Re: Cracked flange on final drive

Post by sjbmw »

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Re: Cracked flange on final drive

Post by two wheel tango »

I brought this on myself for sure.

Before I put the bike in storage for winter last season I removed all the painted parts and the shocks. The plan was to get a paint job done and have the shocks serviced before spring this year.

- Removed all the painted parts.
- Got around to the shocks... pulling them 1 at a time and replacing with the stock shocks was the plan. (which I've done 3 times before in the bikes long history)
- Removed the font shock and got distracted along the way... wife summoned me to help with our 3 year old and 3 month old (at the time).
- Back down in the garage a few hours later and in my haste to close out and put the bike in storage I got to work on removing the rear shock not realizing I had not installed the old front stock shock.
- Long story short the bike ended up tipping over... and I battled to get old shocks back on it and eventually rolled her into storage for the season.
- Everything buttoned back up hand tight.
- Didn't notice the crack then... which I find odd.

Fast forward to spring this year:
- Finally got the painted parts to a body shop for painting a week ago. (looking forward to seeing the finished product next week.)
- Got the shocks back last week... got around to installing this weekend and here I am :(

I'm inclined to repair in place if at all viable. I can find a place to make it happen.
- The bike's just north of a 100K... never an issue with the final drive. Rather do an expedient repair, if possible, than replace. Let it fail if/when it does and tackle replacement from there.

That's my opinion, for now. But I'm not a professional... hope to get more informed opinions and options on how to proceed here...
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Re: Cracked flange on final drive

Post by kirby »

That's a nasty one!
If you take it to a dealer he is going to want to replace, I would be shocked if that wasn't the case.

If you take it to a machine/welding shop they will want it dissembled for Mig/Tig weld because this type of welding is electric and it could (and most likely will) weld the internal gears(and or the bearings) together while trying to weld the case.(+ welding cast parts like this could turn out bad as it tends to make them even more brittle.)

I'd bet that you can find a used unit on ebay or one of the BMW wreckers. I've seen complete low mile engines on E bay for $600 and trans for under $400.
Be patient and find a complete unit and bid on it or buy from someone like beemer boneyard (great folks there). They may even have a case, but if it was me I would buy a complete unit off ebay or someplace like that.

Good luck!
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Re: Cracked flange on final drive

Post by Keppelj »

I'm a welder and would fix this break if I'd done it to myself! Fortunately you have the second flange to help locate the broken one exactly. The piece needs to come off the bike and be stripped of moving parts and cleaned because it will require preheating before TIG welding. Strip it down and find a TIG welder who's confident doing it and I wouldn't hesitate to proceed.
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Re: Cracked flange on final drive

Post by two wheel tango »

Thanks all for the feedback... just a quick update on where I am with this.

Looked into what it would take to disassemble the final drive and get the cracked housing fixed... well beyond my skill level and comfort zone. Sourcing a used final drive (31:11) on eBay can be had but of questionable provenance... and from the listings I followed there's a fair amount of interest and movement... I suspect from GS riders. Beemerboneyard... nothing in stock online but didn't inquire.

In my research I happened across Virginia Motorrad - Spoke to Anton there... they have used housing covers on hand and can repair/ rebuild whatever else needs attention. I plan on pulling the final drive this weekend and shipping it to him for a full service... found a Chris Harris video on removal.. and do have a copy of the shop manual to augment. For the price and peace of mind I reckon this is my best path forward...
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Re: Cracked flange on final drive

Post by towerworker »

I live less than an hour from Anton. He's well respected and well known. I've never had personal dealings with him but a close friend has and he was very pleased. I think you made a good choice.
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Re: Cracked flange on final drive

Post by CycleRob »

two wheel tango wrote:In my research I happened across Virginia Motorrad - Spoke to Anton there... they have used housing covers on hand and can repair/ rebuild whatever else needs attention.
THAT is an excellent, lowest cost, most trusted professional repair. You cannot beat experience, know-how and factory resources.

Welding would be a good choice IF the disassembly, Aluminum welding and reassembly were properly done at a lower cost.
Then you have the deciding fact: "The bike's just north of a 100K... never an issue with the final drive".
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Re: Cracked flange on final drive

Post by two wheel tango »

Just closing the loop on this thread.

Got the final drive serviced and installed without much hassle. Cleaned up a lot of wiring and cracked insulation while I had the bike apart. Finally got her out for the first ride of the season... which was pretty much a test run close to home to make sure all was in order. And on that front all is good.

Dreary day here today... bummed I didn't get to see my new paint job under sunlight.

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Re: Cracked flange on final drive

Post by towerworker »

Looks great!
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Re: Cracked flange on final drive

Post by gregor »

So you went for the weld? Any pictures of the housing when it came back?
Looks great. What's the torque arm spec?
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Re: Cracked flange on final drive

Post by two wheel tango »

gregor wrote:So you went for the weld? Any pictures of the housing when it came back?
Looks great. What's the torque arm spec?
I ended up removing the entire final drive unit and sending it into a shop that specializes in rebuilding them. The part that was cracked was just the housing cover and they actually had used ones on hand... so that piece ended up being a third of the price of getting it new from BMW.

They inspected and rebuilt the final drive back to factory spec while it was opened up. New main bearing, seals etc. I was told that the original factory setup was good and that generally everything was in pretty good nick before they commenced work on it... main bearings lacking some smoothness compared to new but thats about it. The paralever bushings were also in decent condition but ended up having them replaced too... with plastic (nylotrol) bushings.

I think I snapped a pic of just the new bushing before I put the final drive unit back on. Not much to see though but if you're interested I can dig it up and attach here.

Re-install was to BMW spec... have the shop manual and supported by a Chris Harris youtube video on this topic. It was generally painless and hassle free to both pull the final drive out and re-install it.... hope I don't have to touch it again for another 15 years though :D
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