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Uncle Ben's BMW - Final Drive is Toast

12/12/2015

5 Comments

 
If you recall, when I drained the oil out of the final drive I found a bits on the magnetic drain and a chunk of metal that was a wee bit concerning:
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After reading up on airhead final drives, I realized I could remove the inner cover without disturbing the gear setup. (That anti-seize lube crap is a bitch to clean out of the splines!)
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Well I found the rest of it and I was able to put Humpty Dumpty back together again - sorta. I couldn't find a parts diagram for the final drive, so I have no idea what this is, but it looks like it's supposed be a trust washer that is located at the end of the needle bearing in the center of the drive.  
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You can see here there is metal smeared on the shoulder of the flange and there is some blueing from overheating visible too. 
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So this drive is toast. Too bad as the bevel gears actually look very good. This was a 32/11 drive with a ratio of 2.91. It's one of the tallest rears BMW made (I guess the R100S was supposed to be a powerful long range highway cruiser.) I've decided to replace it with a used 32/10 (3.20 ratio) unit off a '73 I found on eBay. This will screw up the speedo drive ratio, but who cares? Bonus is the brake pads are included - I hope they're good enough to use. 
5 Comments
Giuseppe
1/25/2018 04:36:14 am

Hi! I found you post very helpful! ..im aboute to change the big bering inside the final drive.
I have one question: can you tell me the torque value for the tightening of those 10 bolt of the cover? Couldnt find anywhere
Thanks! R100 S 1978

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Doov
1/25/2018 08:23:36 am

I really don't remember. Sorry, I did that work in a flurry of activity. I used Snobum's website a lot. I think pretty much everyhing is on there - somewhere. Try http://bmwmotorcycletech.info/torquevalues.htm.

-- David

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website link
9/21/2020 12:48:19 am

Here I have found impressive techniques and great services with us,thanks for making the more car parts as well. Including the essential services for car techniques and parts as well.

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Cris
7/19/2021 12:28:35 pm

Hello! Why would you consider this drive gone? I saw that the needle bearing inner race was damaged which can be replaced. Or was the whole case damaged as well?

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Doov
7/20/2021 08:11:47 am

Cris, It's been a while, but there was significant blueing (heat damage) as well as a fair amount of galling. I suppose you could have fixed it, but it wasn't worth it to me.

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