135i N55 DCT - Possible to swap in an M3 DCT differential?

MilkBags

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Feb 28, 2018
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2011 135i N55 DCT
Hello,

This seems like the right forums for people attempting to do non-standard stuff so I figured I give this a shot:

I know this topic has been covered a lot for 135i/335i but with MT and some AT but I haven't found any clear answer about DCT with the 2.56 FD.

I read a lot about people who have done it and I know I'd need a custom-made driveshaft, axle shafts as well as the differential from a DCT M3 itself. I can get those easily and for a good price.

I understand the M3 DCT differential has a FD of 3.15 which lines up pretty well with the x35i MT FD of 3.08, but would it work with my 2.56 FD or would it have any issues shifting at the right RPMs? Or any other issues whatsoever? Asking because this person here mentions shifting issues with a 3.08 diff in a N55 DCT. I understand my top speed would be lower with a 3.15 ratio as well, but that's fine.

Thank you!
 
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doublespaces

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Oct 18, 2016
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2009 E93 335i
My understanding is if the ratio is greater than 10% you'll get fault codes. And any difference within that range, you'll get varying up or downshift irregularities depending if your ratio is larger or smaller than what is being expected, with rev matching for example.

There is currently in testing by @jyamona a method to change this ratio, if successful that should solve your problem if I understand his intention correctly.
 
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