E90 M3 Rear Diff Swap

[SliM3]

Hey all I've got a good deal on-the-table for a used E90 M3 6-spd rear diff (3.85:1), and could've sworn I saw something about a swap on the old M3F site but just browsed the thread briefly. Can someone possibly verify that the E90 diff fits the E46 M or at least the ring/pinion set, which is what I really want out of this? TIA

[CrookedCommie]

Yes they are both 210mm. I believe the axle bolt pattern on the E46M is different vs the E9xM so you'd have to find output flanges that work with the E9xM LSD.

[SliM3]

Yes they are both 210mm. I believe the axle bolt pattern on the E46M is different vs the E9xM so you'd have to find output flanges that work with the E9xM LSD.

Awesome, thank you!!

[Daniel]

The m-variable diff on the e9xM is also the same as the E46m

[necm3]

If you take the diff apart now is a good time to get an E36 M3 EVO LSD unit, upgrade it with 4 clutces (about 42% lock) and you will have a really good setup. Big improvement over stock

[DoubleSidedTape]

I have the gears from an e90 m3 (3.85 ratio) in my diff now. I had a local guy rebuild it with a stock LSD and those gears for a really good price, way cheaper than going with the 3.91 gears.

[SliM3]

I have the gears from an e90 m3 (3.85 ratio) in my diff now. I had a local guy rebuild it with a stock LSD and those gears for a really good price, way cheaper than going with the 3.91 gears.

My thoughts exactly!

[DoubleSidedTape]

My thoughts exactly!

Do it then! It's a really nice gearing upgrade without being excessive. 80 mph is around 3200 rpm, and on a lot of roads I can either stick with 3rd or 4th if I want to without shifting depending on how tight the road is. Haven't been back to the track yet.

[ethan]

I have the gears from an e90 m3 (3.85 ratio) in my diff now. I had a local guy rebuild it with a stock LSD and those gears for a really good price, way cheaper than going with the 3.91 gears.

Just want to make sure I understand the combination of parts here. Is that a factory E90 M3 ring and pinion mated to a stock E46 M3 diff and output flanges and mounted in an E46 M3 pumpkin?

[bigjae46]

Just want to make sure I understand the combination of parts here. Is that a factory E90 M3 ring and pinion mated to a stock E46 M3 diff and output flanges and mounted in an E46 M3 pumpkin?

Yes.

I’m in the process of building a 3.73 ZF 4 clutch LSD on my own. Just waiting for a crush sleeve. I over crushed 2 so far. It’s really easy to do.

For my build, I used the shims that came with the donor
E46 diff case. Backlash, carrier preload and gear patter were spot on.