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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Technical Forums > Suspension | Brakes | Chassis > M3 subframe swap questions



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      07-19-2022, 09:42 PM   #1
B58daworld
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M3 subframe swap questions

So I'm aware that it has been done successfully. Installing an m3 subframe in a non-m car And I am planning on doing the same project on my 2006 330xi as i have a rotting subframe. I have read as much about it as I could but there are some things I would like to know as I'm getting into doing custom projects like this. I have a very clean m3 subframe with everything but the differential, and axles.

1st question
The differential.
Is the physical placement of the differential exactly the same? I'm curious if for now I can use my stock diff and drive shaft. I'm hoping I can wait a little longer to get an lsd

2nd question
Wheels
I'm getting new wheels with the project most likely 18x9.5s to clear the brake calipers of the m3. Question is I don't fully understand how to figure out what offset I need. If anyone has done this I would like to know what wheels are being used.

Any help is greatly appreciated!

Last edited by B58daworld; 07-19-2022 at 10:48 PM..
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      07-31-2022, 07:54 PM   #2
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1st question: Your diff and driveshaft should be fine. Please know that the attach points for the toe link on the M3 subframe are not located inboard/outboard as std/non m3 subframe. You will need to run the M3 specific toe links now. They are beautiful aluminum arc shaped. I am unsure if your non m3 spindles (don't know the bmw part term) will accept these toe links or if you must also run the M3 spindles. Good luck and I'll be reading here to see how you make out.
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      08-02-2022, 07:21 PM   #3
B58daworld
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Quote:
Originally Posted by BB_cuda View Post
1st question: Your diff and driveshaft should be fine. Please know that the attach points for the toe link on the M3 subframe are not located inboard/outboard as std/non m3 subframe. You will need to run the M3 specific toe links now. They are beautiful aluminum arc shaped. I am unsure if your non m3 spindles (don't know the bmw part term) will accept these toe links or if you must also run the M3 spindles. Good luck and I'll be reading here to see how you make out.
I will post pictures of the build, with parts diagrams and cost of everything for anyone who would like to follow the build, I work at a bmw dealership so makes it a lot of it easier as far as sourcing parts and information. And by spindles I believe they are known as knuckles. The subframe I purchased came with all the control arms, knuckles, brakes. And it is very very clean, not a spec of rust on the thing, it looks like someone replaced everything, barely drove it and sold it, picked it up for 700 bucks shipped.😀
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      08-04-2022, 04:28 PM   #4
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Quote:
Originally Posted by B58daworld View Post
I will post pictures of the build, with parts diagrams and cost of everything for anyone who would like to follow the build, I work at a bmw dealership so makes it a lot of it easier as far as sourcing parts and information. And by spindles I believe they are known as knuckles. The subframe I purchased came with all the control arms, knuckles, brakes. And it is very very clean, not a spec of rust on the thing, it looks like someone replaced everything, barely drove it and sold it, picked it up for 700 bucks shipped.😀
I just swapped mine and used an 335i diff with Mfactory LSD with stock driveshaft and axles on my 335i. Assuming that the Xi rear is the same as the base it will be fine.

I did use the M3 rear calipers and also did the front swap with a master cylinder swap. If you aren't swapping the front I then the M3 brakes will be too large especially if you don't have the equivlent of the 335i brakes that I started with. I am not sure if the M3 brakes will fit under 18" wheels, I had 19s on the car before the swap.


I didn't really even need an alignment after I did mine. When I took it in they basically didn't change anything after swapping the full front and rear including the front steering rack.

-Rich
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      08-05-2022, 05:39 AM   #5
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Quote:
Originally Posted by B58daworld View Post
I am planning on doing the same project on my 2006 330xi as i have a rotting subframe.
Out of curiosity, can you explain how an aluminum subframe can rot?
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      08-05-2022, 07:39 AM   #6
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The rear subframe is steel...
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      08-05-2022, 07:50 AM   #7
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Quote:
Originally Posted by david in germany View Post
Out of curiosity, can you explain how an aluminum subframe can rot?
The rear subframe is steel. I went to do my alignment one day and the metal tabs that keep the eccentric bolts in place completely be disintegrated. So can't do my alignment, going through tires atleast once a year. I believe the front subframe is aluminum though. So I'll keep it for now
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      08-05-2022, 11:34 AM   #8
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Quote:
Originally Posted by B58daworld View Post
The rear subframe is steel. I went to do my alignment one day and the metal tabs that keep the eccentric bolts in place completely be disintegrated. So can't do my alignment, going through tires atleast once a year. I believe the front subframe is aluminum though. So I'll keep it for now
The m3 front isn't compatible because its engine mounts are setup for the V8.

The control arms can be swapped but not the subframe.
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      08-05-2022, 03:02 PM   #9
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Quote:
Originally Posted by B58daworld View Post
The rear subframe is steel. I went to do my alignment one day and the metal tabs that keep the eccentric bolts in place completely be disintegrated. So can't do my alignment, going through tires atleast once a year. I believe the front subframe is aluminum though. So I'll keep it for now
Sorry, I was thinking front.
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      08-05-2022, 04:18 PM   #10
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Quote:
Originally Posted by B58daworld View Post
The rear subframe is steel. I went to do my alignment one day and the metal tabs that keep the eccentric bolts in place completely be disintegrated. So can't do my alignment, going through tires atleast once a year. I believe the front subframe is aluminum though. So I'll keep it for now
Usually is the tab for the toe link. Two option other than replacing the subframe: weld on bracket for the eccentric bolt, or aftermarket toe links with lock down plates and bolts. I'm suggesting these because often subframe swap will open more headaches, like rusted brake lines that can't disconnect, and also a lot of money. Just so you can see: https://www.langracing.com/e30-bmw-r...er-adjustment/https://garagistic.zendesk.com/hc/en...tions-Overview
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      08-05-2022, 05:57 PM   #11
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Quote:
Originally Posted by feuer View Post
Usually is the tab for the toe link. Two option other than replacing the subframe: weld on bracket for the eccentric bolt, or aftermarket toe links with lock down plates and bolts. I'm suggesting these because often subframe swap will open more headaches, like rusted brake lines that can't disconnect, and also a lot of money. Just so you can see: https://www.langracing.com/e30-bmw-r...er-adjustment/https://garagistic.zendesk.com/hc/en...tions-Overview
It sounds like the frame wont have any solid steel left to weld to...

In that case replacing it all makes sense but I agree it will likely mean that all of the brake lines will also need to be replaced if there is that much rust.

(so glad I moved out of the rust belt).
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      08-07-2022, 08:42 AM   #12
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Quote:
Originally Posted by rbryantaz View Post
I am not sure if the M3 brakes will fit under 18" wheels, I had 19s on the car before the swap.

-Rich
18” rims were standard on some e92m3’s Style 219M and 260M. I also know a bunch of guys tracking them on 18” rims and one on 17” Apex ARC 8’s. So 18” definitely can work.
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      08-07-2022, 04:34 PM   #13
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Quote:
Originally Posted by feuer View Post
Usually is the tab for the toe link. Two option other than replacing the subframe: weld on bracket for the eccentric bolt, or aftermarket toe links with lock down plates and bolts. I'm suggesting these because often subframe swap will open more headaches, like rusted brake lines that can't disconnect, and also a lot of money. Just so you can see: https://www.langracing.com/e30-bmw-r...er-adjustment/https://garagistic.zendesk.com/hc/en...tions-Overview
I did consider welding new tabs in place and calling it a day, we have a bodyshop with excellent welders. But i thought about it and said to myself, " but what fun is that?". I always enjoy a project, keeps me busy from the wife. And I would like to keep the vehicle long term and just have it as a toy for when im ready to do an engine/ trans swap.
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      08-07-2022, 04:38 PM   #14
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Quote:
Originally Posted by rbryantaz View Post
It sounds like the frame wont have any solid steel left to weld to...

In that case replacing it all makes sense but I agree it will likely mean that all of the brake lines will also need to be replaced if there is that much rust.

(so glad I moved out of the rust belt).
so I actually already had a brake line go in the rear, so i replaced all the brake lines ( soft and hard) on the subframe side. It is quite frustrating because not sure if I should swap them over considering they are brand new or just leave the lines on the subframe as they are. But I will be replacing the rest of the lines once I have the subframe out such as the long lines from ABS to Rear subframe and I'm going to go ahead and replace the fronts as well. Just for peace of mind.
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      08-07-2022, 04:45 PM   #15
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Quote:
Originally Posted by Biginboca View Post
18 rims were standard on some e92m3s Style 219M and 260M. I also know a bunch of guys tracking them on 18 rims and one on 17 Apex ARC 8s. So 18 definitely can work.
I know 17 apex work, and I know just about any 18s will work. My question is, how to decide which offset will work/look best. I see some guys do the same offset front and rear, I see some people do different offset front to rear. How do I find out which offset will look best so I don't purchase a set and think I should've gone with a different offset. I am assuming with all wheel drive I really should go with same offset front to rear. Even still how do I decide sat Et31 vs Et38 for example will look best. This project will already cost a good chunk of change and I don't wanna have to get multiple sets of wheels to find the ones I need. Part of it is personal taste which I understand too. But simpler question i suppose is what offset would work with non M body so the wheels dont rub. I may lower the car by an inch, undecided at the moment
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      08-08-2022, 01:42 PM   #16
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Quote:
Originally Posted by B58daworld View Post
so I actually already had a brake line go in the rear, so i replaced all the brake lines ( soft and hard) on the subframe side. It is quite frustrating because not sure if I should swap them over considering they are brand new or just leave the lines on the subframe as they are. But I will be replacing the rest of the lines once I have the subframe out such as the long lines from ABS to Rear subframe and I'm going to go ahead and replace the fronts as well. Just for peace of mind.
The lines are easy to change if you have the subframe out and they aren't rusted.

The rear M3 and 335i rear lines were exactly the same. The fronts are different and have different brackets and rubber mounting points for the brackets. The M3 also has better subframe brackets. Solid aluminum bushings (like the latest cars) are better but the M3 bushings are much stiffer than the normal ones.

-Rich
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