BMW E9X M3 Subframe w/ LSD Retrofit for my 335i

June 8, 2023 Samuel Abraham

One of the biggest upgrades I had been planning for my 335i since upgrading the turbos, was to swap in an E9X M3 rear end. For the power I wanted to make the M3 DCT rear end with the 3.15 ratio LSD would be perfect. One might ask, why not just buy a Quaife LSD and install that into the existing 335i differential pumpkin? Well, the entire cost of this swap doesn't end up being much more than JUST a drop in LSD, AND you end up getting much much more. I wasn’t planning on doing this any time soon, but when @kurd.e92 sent me an offer I couldn’t refuse back in July, I jumped on it. In August I took the ML63 up to NorCal for Monterey car week with @vizucars, and we picked up the subframe. All of us managed to squeeze the complete subframe in the back of the ML.

Here's the old dusty 335i subframe after lowering it out of my car. All the sand from a dry lakebed run I did years ago... I'm STILL finding sand everywhere lol.

This massive upgrade includes larger M3 rear brakes, aluminum M control arms, a 10mm thicker sway bar, beefier driveshaft and axles, along with the LSD. @daddyjimmy helped Aiden, my dad, and I get that subframe out of the ML and into my backyard where it would sit until I was ready to refresh it and install it into my E92. In September, I blew the factory 335i 6AT diff (paired to the 6MT). With just over 1k miles on the new turbos I installed in Dec ‘21, the car was once again un-drivable. So, during my winter break in Dec ‘22, I installed some solid aluminum Turner Motorsports subframe mounts and Powerflex poly diff mounts into the M3 subframe in my backyard. By the way, pretty much every M car since the F10 M5 has had solid subframe mounts from factory! Thanks to @s85_maniac for letting me borrow his bushing tools! I rolled the subframe over to my garage and swapped in the subframe at around 3am. A big job nearly complete, however I still had to deal with the driveshaft. When swapping in an E9X M3 rear end to an N54 powered car, you need to modify the M driveshaft to be the correct length/CV. This is more traditionally done by shortening one end of the E9X M3 driveshaft, as it is beefier than the stock 335i one. However, after seeing a post by @1spool, I was convinced I might as well do an F8X M3/M4 one piece carbon fiber driveshaft... That’ll be the next post!

I'll be making a more detailed video on this swap in the near future, talking about what's needed, what I recommend doing "while you're in there," and the overall steps.

It'll be posted to my YouTube channel @SamAbraham

Take a look at some of the pics/videos throughout the process! Some things I noticed while having the subframes side by side: The M3 subframe seems more substantial and overall beefier. The axles are certainly larger in diameter, and should hold up much better to the low-end torque my upgraded turbos will throw at them. The aluminum control arms off the M3 are far more substantial than the 335i flimsy pressed steel arms. They even have some M logos on each of the arms which is kinda cool, as pretty much no one would see them. Sadly I had to transfer over my 335i spring perch arms because I use 335i coilovers, but some day I'll get M3 rear coilovers and put the M3 perches back on. The diff pumpkin as a whole is MUCH larger off the M3 when compared to the 335i... AND it has some pretty cool looking (and functional cooling fins) at the bottom! Perhaps a diff cooler can also be mounted to the rear bumper in the future... Kinda like an AMG Black Series model haha.

Turner Motorsports Aluminum E9X M3 Subframe Mounts: