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      06-30-2019, 10:30 PM   #1
chris_flies
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2009 BMW 128i  [5.00]
Complete Differential Rebuild DIY

I want to eventually do a DIY guide on this, if I end up doing it, but I needed to ask some questions first:

My differential recently blew on my 128i. It was a 3.73:1 diff from an auto car, with an MFactory 1.5-way LSD swapped for the open diff center section. The ring gear bolts backed-off and completely ruined the diff's internals (thankfully the LSD looks untouched). A window was blown open in the back cover and oil evacuated the diff while driving at 70mph. The bearings were destroyed from lack of lubrication while it was limped home 2 miles, and the ring gear teeth contacted bolts, and the gear action is extremely rough.

My intentions are to buy another auto diff ($100 or so) and rebuild it to like-new condition internally (mostly replacing bearings). Has anyone rebuilt a differential here? Was there a certain kit you used? Is it a job someone with good technical knowledge and know-how can do in a home garage? I built the LSD myself, but elected to not replace the bearings (something about biting-off more than I could chew), and now I'd like to, at a minimum, replace the main side bearings, and I'd also like to replace the pinion bearings if it isn't too complex of a job.

Any help/input is greatly appreciated.

Thanks,
Chris
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      07-01-2019, 12:11 PM   #2
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I remember a couple of old threads saying the bearings were impossible to get, I would start my search/research there. Hopefully things have changed over the years and you can find these now though.
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      07-02-2019, 07:53 AM   #3
JimD
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Chris,

You've done so much to your car I think you can do it. But you will need a sturdy press to replace some of the bearings. My son rebuilt the rear end of his 42 year old pickup in his garage including setting the backlash and getting the gear engagement right. He broke the pinion. He is on his second type of limited slip and changed those himself. So with the right tool and some mechanical ability is is fully possible to do it yourself.

I looked at this briefly to see if my son's Ford pickup experience seems reasonably applicable to BMWs:

https://www.eeuroparts.com/blog/1076...l-rebuild-diy/

I decided they are pretty similar, ignoring the fact that pickups are solid axles. The article recommends just taking it out yourself and letting somebody else press the bearings in place and set the backlash. That would be an option. My son found that process frustrating but he got it done. You have to try different shims and the assembly process to make the test is not terribly easy. But he got it done and it works fine.

I agree about checking on parts availability although I suspect they can be found. Car manufacturers do not make caged bearings and the suppliers who do make them have catalogs. A quick google search also showed some rebuild kits but I did not look at them closely enough to see if they are applicable.

Jim
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      07-02-2019, 09:57 AM   #4
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Yeah, going back that post about not having bearings was from ages ago. I see now posts where MFactory says they can provide shim kits and new bearings for sale as well.

Not sure how sour your feelings are with them but...
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      07-02-2019, 10:40 AM   #5
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Quote:
Originally Posted by dtla1 View Post
Yeah, going back that post about not having bearings was from ages ago. I see now posts where MFactory says they can provide shim kits and new bearings for sale as well.

Not sure how sour your feelings are with them but...
Diffsonline has shim kits and bearings.
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      07-04-2019, 10:56 PM   #6
iminhell1
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I bought output shaft bearings from England. I wanted to stick with the OE ball bearing vs the US sold roller bearing.

You'll have to verify if a kit is available for you but, https://www.ebay.com/itm/462014810-I...bSfd1mhwDAXm2A

I used the part numbers listed to get the output shaft bearings.
Which I now have just sitting since my problem wasn't bearings, as we now know.

Mike at MFactory had no idea about these kits until I told him month or so back.
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