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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Technical Forums > Suspension | Brakes | Chassis > M3 Rear Subframe Swap to E91 E90?



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      11-17-2019, 02:36 AM   #1
Soravia
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M3 Rear Subframe Swap to E91 E90?

I have no idea which if it came from E90 or E92 M3. But it is M3 rear subframe and rust free with good bushings.

Will it fit? I can get it pretty cheap and will save me having to take off rust or replace/upgrade frame bushing and diff bushings.

I plan to drop the subframe with all the work I'm doing to take care of the salt rust. Not too bad but it's on many different parts and replacing or repainting will prevent it from getting too far.

Thanks.
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      11-17-2019, 03:26 AM   #2
Tambohamilton
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Yep, it'll bolt right in. Great upgrade
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      11-17-2019, 04:33 AM   #3
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Quote:
Originally Posted by Tambohamilton View Post
Yep, it'll bolt right in. Great upgrade
+1
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      11-17-2019, 05:16 AM   #4
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Just a thought - the m3 subframe does need one of the suspension arms to be the m3 arm. The mounting point is in a different location, so the non-m arm doesn't fit. I can't remember right now which one it is.
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      11-17-2019, 08:46 AM   #5
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Quote:
Originally Posted by Tambohamilton View Post
Just a thought - the m3 subframe does need one of the suspension arms to be the m3 arm. The mounting point is in a different location, so the non-m arm doesn't fit. I can't remember right now which one it is.
Are you talking about the lower control arm where the rear damper and springs are mounted to?
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      11-17-2019, 08:53 AM   #6
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Hmm.. M3 rear lower back toe arms don't bolt on to non-M rear wheel hub spindle, I read. So I blew $60 on two of those. I'll have to get aftermarket adjustables for $120 later.
I'll check on it later today when I jack the car for rear winter wheels.

I can't tell the difference between the two, aside from bushings and the welds. M3 has more welds and not using the same stamped steel?
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Last edited by Soravia; 11-17-2019 at 01:38 PM..
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      11-17-2019, 02:06 PM   #7
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https://bmw.***********.com/threads/...mponents.4861/

Remotely related but I saw this 535xi guy swapped in M5 and 535i RWD REAR sub frames, along with lots more stuff.
Lots of aluminum subframes, front and back for 5 series. Still a pork with 3,900 lbs even with all the aluminum bits and RWD conversion.
There's 13lbs difference EACH for AWD cast iron front spindle vs RWD front cast aluminum knuckle, without shafts, front diff, transfercase, and steel vs aluminum sub frame.

I ordered the first picture M3 sub frame. Will see how it goes in.

Also tempted to get M5 aluminum rear sub frame. But I know it won't go into the car.

Last edited by Soravia; 11-18-2019 at 07:50 AM..
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      11-18-2019, 02:36 PM   #8
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$30 E90 M3 rear guide rod, camber control arms came in, but for ONE side. LoL
Online shows only these numbers for sale. I'll call and ask if they have the other side.
Centric is the brand but I'm sure someone is make them for the brand. Someone who makes them for OE BMW supply 😃
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      11-18-2019, 03:45 PM   #9
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If there are suspicious grind marks next to the part number on the casting, the chances are that's where the BMW logo has been removed. I'm pretty sure TRW would be OE.
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      11-18-2019, 04:39 PM   #10
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I could be crazy, but I thought one of the dif mounting points were different on the M3 subframe. Also, the toe arms and whatever the arm is called that holds the rear springs.
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      11-18-2019, 04:47 PM   #11
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I'm 90% that all arms are interchangeable between m and non-m (with correct shock mounts etc), except the toe arms.

The m diff bolts into a non-m subframe (given correct driveshafts etc), so that part is safe the other way around too.
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      11-18-2019, 05:58 PM   #12
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100% the M dif does not bolt into the non-M subframe. That is why anyone who wants to upgrade to the M dif needs the whole subframe.

So OP would also need the M dif, then adapted drive shaft.
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      11-18-2019, 07:04 PM   #13
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M Diff definitely needs M shaft to go into it.
But I think I read diff mounts the same, just the cover is different. Looks the same mounts to me.

As for M toe arms. I have them. They are one inch shorter vs non M toe arms. This is probably because M uses different King pin aka spindle in the back axle, and reaches in closer? Either way if the sub frame mount was where the issue is I got it covered for $60 😃.

I can get M Diff for $700 range I think. Welding the OE rear shaft to fit M Diff will be required.

If M spring/damper arm can go in, I might be tempted to put it in with adapter for my Bilstein B6 wagon dampers.
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      11-18-2019, 07:29 PM   #14
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Just called that number for Centric, got to product guy quickly. He says his system is wrong and keeps saying same part for left and right. He will ask his suspension guy tomorrow to check it out and email me back. I'll call to follow up.
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      11-18-2019, 08:08 PM   #15
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Quote:
Originally Posted by weehe126 View Post
100% the M dif does not bolt into the non-M subframe. That is why anyone who wants to upgrade to the M dif needs the whole subframe.

So OP would also need the M dif, then adapted drive shaft.
https://www.e90post.com/forums/showthread.php?t=1365817
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      11-18-2019, 08:32 PM   #16
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I have that thread book marked as well.
I'm not making that power so I'm OK without all the work of conversion. I'll put in $750 Torsen LSD later on the car. Much later on. AWD makes less off necessity for bigger shafts, and I don't have tire like RWD coupe to grip anyway.
M3 bushings should take the standard diff housing just fine.
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      11-18-2019, 10:55 PM   #17
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I verified that M3 and 3 series use the same rear lower forward trailing arm, the one that looks like a ladder. Checked it on RMEuropean
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      11-19-2019, 02:24 AM   #18
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Quote:
Originally Posted by Soravia View Post
I have that thread book marked as well.
I'm not making that power so I'm OK without all the work of conversion. I'll put in $750 Torsen LSD later on the car. Much later on. AWD makes less off necessity for bigger shafts, and I don't have tire like RWD coupe to grip anyway.
M3 bushings should take the standard diff housing just fine.
Yeah, it's a handy thread. My point was that he didn't need to fit the m3 subframe with the diff, so you'll also be fine with a non-m diff in the m3 subframe.
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      11-21-2019, 10:10 PM   #19
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Sub frame came in. Will open it up this weekend, maybe
Small enough to fit in with seats folded on sedan or Wagon, maybe coupes, too.
About 40+ lbs is my guess.
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