Manual to auto differential ratio swap

[desertman123]

So I understand the 128i comes with a 3.23 in the manual trans, but in the auto it comes with a 3.73.

Is it as simple as buying a diff from an auto 128i, dropping mine and tossing the new one in there? Because if so, that's a pretty easy way to add acceleration for like $200.

Fill me in on the info I'm missing.

[Eins Suchtig]

I'm playing with the idea.

Does anybody know if a 328i auto 3.73 pumpkin (part no 33107566179 ) will be a simple bolt on into a 2011 manual 128I?

My concern is that real OEM lists the 3.73 auto diff for 128i as 33107591108, so there must be a difference between 128i and 328i auto diffs.

Down here 128i is uncommon, 328i are everywhere...

Thanks

[gixracer]

Originally Posted by Eins Suchtig

I'm playing with the idea.

Does anybody know if a 328i auto 3.73 pumpkin (part no 33107566179 ) will be a simple bolt on into a 2011 manual 128I?

My concern is that real OEM lists the 3.73 auto diff for 128i as 33107591108, so there must be a difference between 128i and 328i auto diffs.

Down here 128i is uncommon, 328i are everywhere...

Thanks

Drops right in, the auto pumpkins are small and so are 128 manuals. I have a 3.91 pumpkin and compared them when I did my swap for clarification. I had to verify because I swapped 135 rear complete hub assemblies with my 128i. I now have 135i rear hub assemblies with 328i rear half shafts mated to my stock 128i pumpkin. I just need to get my diff done with lsd and I'd be mint but the s65 project is eating up what little time I have.

You will love the ratio swap

[mad1stgen]

Originally Posted by gixracer

You will love the ratio swap

He's not lying

I've been running 3.73s for a week now, it's been fun. The engine is always in power band it seems. It's a direct, 2hr swap. Do it, you won't regret it.

I used a differential part number 33107566179 out of 2011 E91. My car is a 2012 128i 6MT.

[Eins Suchtig]

Thanks all! Let's start the hunt!