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      08-17-2020, 12:38 PM   #1
alairealtois
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Manual to Auto Diff Conversion

So I read that all Non DCT automatic 135iís have bolted in diffs, as opposed to being welded, would it be easier to just buy a rear end or pumpkin from a wrecked auto car, and replace my welded one with the donor? Is it possible and what other parts would be needed besides just the pumpkin?
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      08-18-2020, 02:52 PM   #2
The Wind Breezes
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First, it's not clear what you mean by "bolted in diff". The diffs are all "bolted in" to the subframe so I'll make the assumption that you're referring to the way the ring gear is attached.

You don't mention why you need to do any of this. One can guess, but more context would be nice.

DCT, auto, manual diffs on 135i are each a different ratio. Your gearing would change pretty significantly.

Also the cheap LSD you think you want probably isn't that great and will do nearly nothing for your probable intended uses (leave 2 strips and spin in a parking lot a couple times a year) that the stock brake system doesn't already do. Clutch type or go home. Alternatively you could give the diff 100% 2-way lockup for about $30 if you have a welder and that beats the shit out of any geared diff (the cheap kind).
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      08-19-2020, 02:47 PM   #3
alairealtois
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i have a 2012 135i DCT, im looking to do a drag build, (nice big tires, bigboost turbo kit etc.) but i know the ring gear is welded on, ive read the ring gear for the AT 1's have bolted in ring gears which makes it easier to drop in an LSD for the purpose of doing hard launches at a prepped track.

no need for hostility. so would swapping the rear ends and putting the LSD in the new donor pumpkin be basically plug and play? i'm okay with going up gear ratios top speed isnt really what im after.
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      08-19-2020, 05:32 PM   #4
The Wind Breezes
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Welded diff is superior to LSD for your application. I daily drive one on the same car you have with minimal drama and lots of fun so a full lockup for a car specialized toward drag racing is sort of a no brainer.

I am passionate about good / bad hardware and installs being well thought out. Don't take that the wrong way! I love all car enthusiasts especially if they have the good taste to put more power in the car and drag race it as you are doing.
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      04-16-2024, 10:19 AM   #5
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Quote:
Originally Posted by alairealtois View Post
So I read that all Non DCT automatic 135iís have bolted in diffs, as opposed to being welded, would it be easier to just buy a rear end or pumpkin from a wrecked auto car, and replace my welded one with the donor? Is it possible and what other parts would be needed besides just the pumpkin?
Hi, checking the feasibility of this, any luck ?
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      04-18-2024, 11:43 AM   #6
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Automatics have a different ratio. It's 3.46 vs 3.08. I have the MFactory auto LSD in my 6MT car. Lots of TQ!
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      05-02-2024, 11:05 AM   #7
Eyeman
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Garage List
Old thread. I don't know about the switch. I do know that it was easier to get a mechanical LSD for me since my car is an auto. I also know that my Quaife works great. No more spinning one tire and barely moving because traction control has kicked in.
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