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E46 M3 (2001-2006) Engine: S54 - Max Hp: 333 hp at 7,900 rpm / 262 lb/ft at 4,900 rpm
Total Produced: 45,000+ - Years Produced: 2001 to 2006.


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Old Thu, May-14-2015, 06:34:55 PM   #1
Amadeus
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Default Subframe: Front vs. Rear mount brace

I have decided to reinforce my rear subframe mounts with a setup similar to this bolt through design: (courtesy 02PRUV)




Now the question is, what to do about the front subframe mounts? Under high torque situations, the rear mounts pull down while the front mounts push upwards. I have seen plenty of pictures of cracks in the front mounts. As I am going to have my rear support welded, is there anything I should do for the front? Of course there is always the reinforcement plate kits, and I will use these if I must - but I'm looking for something better. Are there any custom designs out there that consider some sort of bracing for the front mounts? Maybe even just an additional plate that runs the width of the car? Any input appreciated
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Old Thu, May-14-2015, 06:45:19 PM   #2
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Default Re: Subframe: Front vs. Rear mount brace

Why are you looking for something better?

(Also, why did you weld that horrible monstrosity across the mounts that basically never fail in an E46 M3?)
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1989 M3 Alpinweiß/Black - S62B50 in progress...

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Old Thu, May-14-2015, 06:54:01 PM   #3
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Default Re: Subframe: Front vs. Rear mount brace

The reinforcement plate kits really only spread out the stress on the mounts by increasing the surface area under force. While it may hold up for many applications, they have still been shown to fail. The design above gets at the heart of the issue by distributing it directly to the frame rail.

Lol mounts that basically never fail? Are you aware the subframe issue with the E46? That "monstrosity" is probably most robust fix I've seen so far. Apart from integrating some sort of roll cage.
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Old Thu, May-14-2015, 07:23:51 PM   #4
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Default Re: Subframe: Front vs. Rear mount brace

Quote:
Originally Posted by mgp333 View Post
Lol mounts that basically never fail? Are you aware the subframe issue with the E46? That "monstrosity" is probably most robust fix I've seen so far. Apart from integrating some sort of roll cage.
I don't think that alone will help with the rear subframe cracking...
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Old Thu, May-14-2015, 07:26:47 PM   #5
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Default Re: Subframe: Front vs. Rear mount brace

Quote:
Originally Posted by mgp333 View Post
The reinforcement plate kits really only spread out the stress on the mounts by increasing the surface area under force. While it may hold up for many applications, they have still been shown to fail. The design above gets at the heart of the issue by distributing it directly to the frame rail.

Lol mounts that basically never fail? Are you aware the subframe issue with the E46? That "monstrosity" is probably most robust fix I've seen so far. Apart from integrating some sort of roll cage.
The problem is that the carrier rips out of the sheet metal on the bottom of the car. The re-enforcement pictured is really just sitting on cosmetic metal (unless there are cuts to the bolt carriers we can't see).

Anyhow, to answer your question, just get some metal plates between the subframe and the body to distribute the compression.

If you're really getting happy with the welder over there, another thing I've seen done on full race builds is to weld additional cross-members from the subframe to other (custom) body mounts
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Old Thu, May-14-2015, 08:03:48 PM   #6
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Default Re: Subframe: Front vs. Rear mount brace

Quote:
Originally Posted by mgp333 View Post
The reinforcement plate kits really only spread out the stress on the mounts by increasing the surface area under force. While it may hold up for many applications, they have still been shown to fail. The design above gets at the heart of the issue by distributing it directly to the frame rail.

Lol mounts that basically never fail? Are you aware the subframe issue with the E46? That "monstrosity" is probably most robust fix I've seen so far. Apart from integrating some sort of roll cage.
It's far from one of the most robust fixes that I've seen. It adds a whole bunch of sheet metal in a way that isn't particularly structural. If you really want to cut up your trunk, look at the Randy Forbes Z3 reinforcement design for a better solution. Replace the whole thing and do it cleanly. Instead, you've basically just slapped that crap on top. It's hideous, unnecessary, and of dubious effectiveness.

And yes, I've personally repaired/reinforced a fair number of E46 subframe mounts. What I have consistently seen is that in the later cars, BMW reinforced the rear mounts, which transferred the point of failure to the front.
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2006 GMC Sierra 2500HD 4WD - Duramax LBZ/Allison
2002 BMW M3 Alpinweiß/Black - Konis, AS SSK, JBL MS-62C, IDQ-12v3, JBL MS-8
1999 323i KP/GTS2 Alpinweiß - Hood-in-the-windshield mod
1995 M3 Dakargelb/Black - S50B32/S6S420G, Diffsonline 3.91, H&R/Bilstein, Hotchkis, AS SSK, etc...
1990 325is Brilliantrot/Tan - GC/Bilstein, Sway
1989 325is Alpinweiß/Black - Decontenting...
1989 M3 Alpinweiß/Black - S62B50 in progress...

Hers: 1996 Porsche 911 Turbo Black/Black - UMW LTW Flywheel, Bilstein
Hers: 1988 325iX Coupe Diamondschwartz/Black 5spd - Korman lengthened front driveshaft, 272 cam, H&R/Bilstein

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Old Thu, May-14-2015, 08:22:40 PM   #7
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Default Re: Subframe: Front vs. Rear mount brace

Quote:
Originally Posted by nrubenstein View Post
It's far from one of the most robust fixes that I've seen. It adds a whole bunch of sheet metal in a way that isn't particularly structural. If you really want to cut up your trunk, look at the Randy Forbes Z3 reinforcement design for a better solution. Replace the whole thing and do it cleanly. Instead, you've basically just slapped that crap on top. It's hideous, unnecessary, and of dubious effectiveness.

And yes, I've personally repaired/reinforced a fair number of E46 subframe mounts. What I have consistently seen is that in the later cars, BMW reinforced the rear mounts, which transferred the point of failure to the front.
Explain how is that not structural? It is even more minimalistic than many of the x-bar engineering designs that I've seen. For example



This what you're talking about?


Granted, Forbes Z3 mod is very nice. However, I do not see what his design accomplishes that this does not. Plus his only deals with the rear.

Not sure about newer M3's reinforcing the rear maybe you're right, but I have a 2002 anyway. I am looking for solutions/suggestions for reinforcement for the front subframe mounts.
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Old Thu, May-14-2015, 09:13:20 PM   #8
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Default Re: Subframe: Front vs. Rear mount brace

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Originally Posted by nrubenstein View Post
Instead, you've basically just slapped that crap on top. It's hideous, unnecessary, and of dubious effectiveness.
Ssssshhh... Put the ego away for a sec, and read his post. He's actually going all the way through the subframe carriers to the "crap on top".
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Old Thu, May-14-2015, 09:27:25 PM   #9
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Default Re: Subframe: Front vs. Rear mount brace

Quote:
Originally Posted by Drewster View Post
Ssssshhh... Put the ego away for a sec, and read his post. He's actually going all the way through the subframe carriers to the "crap on top".
And:

1) It's installed in a hideously ugly manner that is difficult to undo.
2) It would be a lot more structurally sound if it were installed properly.
3) It's still welded to thin sheet metal in the rails. Mounting it remotely from the subframe just puts leverage on it.
4) Unless he has a giant turbo, all of this work is completely unnecessary and stupid.
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[B]2011 BMW M3 (E90) Alpinweiß/Cloth - Slicktop stripper, TCK D/A Konis, AS SSK
2006 GMC Sierra 2500HD 4WD - Duramax LBZ/Allison
2002 BMW M3 Alpinweiß/Black - Konis, AS SSK, JBL MS-62C, IDQ-12v3, JBL MS-8
1999 323i KP/GTS2 Alpinweiß - Hood-in-the-windshield mod
1995 M3 Dakargelb/Black - S50B32/S6S420G, Diffsonline 3.91, H&R/Bilstein, Hotchkis, AS SSK, etc...
1990 325is Brilliantrot/Tan - GC/Bilstein, Sway
1989 325is Alpinweiß/Black - Decontenting...
1989 M3 Alpinweiß/Black - S62B50 in progress...

Hers: 1996 Porsche 911 Turbo Black/Black - UMW LTW Flywheel, Bilstein
Hers: 1988 325iX Coupe Diamondschwartz/Black 5spd - Korman lengthened front driveshaft, 272 cam, H&R/Bilstein

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Old Thu, May-14-2015, 07:40:51 PM   #10
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Default Re: Subframe: Front vs. Rear mount brace

Maybe I should have explained the bracing in the picture. There are two long bolts that run through the welded cylinder/tubes all the way down directly to the subframe bushing. You can see the head of the bolts if you look at the picture closely. They are nutted from underneath. As the rear subframe pulls down on the bolts, the force is distributed to the top of the cylinders and subsequently to the frame rails in the trunk area. In addition, the brace is directly welded to the box section between the sheet metal underneath the car and sheet metal in the trunk.

Quote:
Anyhow, to answer your question, just get some metal plates between the subframe and the body to distribute the compression.
Can you elaborate on this, between the subframe and body? How does this differ from the typical reinforcement plates?
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Discussing Subframe: Front vs. Rear mount brace in the E46 M3 (2001-2006) Forum - Engine: S54 - Max Hp: 333 hp at 7,900 rpm / 262 lb/ft at 4,900 rpm
Total Produced: 45,000+ - Years Produced: 2001 to 2006. at BMW M3 Forum.com (E30 M3 | E36 M3 | E46 M3 | E92 M3 | F80/X)