How is this subframe crack?

[AussieE46M3]

Just purchased both the underside plates and the racp rail plates from cmp for the cavity in the trunk. Hopefully that's a good enough set for a daily and leaves room for a stable bar across the rear shocks in the future maybe for a better reinforcement. Thank everyone in the chat for discussing, as I was literally on my way to tackle number 2 of 3 in E46 bulletproofing. I happen to read on and noticed aussiee46 business and loves the idea. I'll let you guys know the end result. Thanks for the help.

Thanks for your business! This was dispatched this morning so hopefully it will be with you soon enough!

[Drewrivera]

Just purchased both the underside plates and the racp rail plates from cmp for the cavity in the trunk. Hopefully that's a good enough set for a daily and leaves room for a stable bar across the rear shocks in the future maybe for a better reinforcement. Thank everyone in the chat for discussing, as I was literally on my way to tackle number 2 of 3 in E46 bulletproofing. I happen to read on and noticed aussiee46 business and loves the idea. I'll let you guys know the end result. Thanks for the help.

[AussieE46M3]

a lot of good info. Spoke with Cayn on facebook and very helpful. I just need to go take a welding class before I try tackling this job!

Glad I could help mate! Feel free to buzz me again if you need any input during the prep/fab.

[Jersey_M3]

a lot of good info. Spoke with Cayn on facebook and very helpful. I just need to go take a welding class before I try tackling this job!

Exactly what I did, good luck to you sir!

[Tonggi]

a lot of good info. Spoke with Cayn on facebook and very helpful. I just need to go take a welding class before I try tackling this job!

[AussieE46M3]

Awesome, thanks for answering all my questions. You've been a big help! I'll get in contact come December; definitely looking for all three reinforcements, and maybe the brace.

No worries mate. Glad I was able to help.

Feel free to reach out to me if you have any other questions in future.

[01SG]

Hey mate,

The chassis rail plates are included within the topside beam kit.

The brace does technically add further strength to the subframe mounts however, isn't necessary to prevent failure. If you want the back end race car stiff then go for it. Down to personal preference IMO.

I'd suggest solid bushings as they really do make the car feel a lot more responsive and direct in the back end. If you're wanting to keep stock ride height/camber arms and not raise the subframe then I would say the brand is not significant as they are all very similar so I'd go by which is most competitively priced among the reputable brands.

Not a problem. feel free to message me if you ever want to discuss anything further.

Awesome, thanks for answering all my questions. You've been a big help! I'll get in contact come December; definitely looking for all three reinforcements, and maybe the brace.

[AussieE46M3]

Just to be absolutely clear, to fully address the issue with your kit, it would consist of the underside plates, topside beam kit, front mount extension, and rail plates? Or are the rail plates not needed with the bar?

Also, would you recommend the 6 point brace for a weekend car with, at this moment, limited track use?

And to bother you one last time, what bushings would you suggest at stock ride height? Prefer to keep the cheap stock camber arms for now as well. I'm between stock, or Turner.

Thanks for your time; definitely looking forward to placing an order.

Hey mate,

The chassis rail plates are included within the topside beam kit.

The brace does technically add further strength to the subframe mounts however, isn't necessary to prevent failure. If you want the back end race car stiff then go for it. Down to personal preference IMO.

I'd suggest solid bushings as they really do make the car feel a lot more responsive and direct in the back end. If you're wanting to keep stock ride height/camber arms and not raise the subframe then I would say the brand is not significant as they are all very similar so I'd go by which is most competitively priced among the reputable brands.

Not a problem. feel free to message me if you ever want to discuss anything further.

[01SG]

Just to be absolutely clear, to fully address the issue with your kit, it would consist of the underside plates, topside beam kit, front mount extension, and rail plates? Or are the rail plates not needed with the bar?

Also, would you recommend the 6 point brace for a weekend car with, at this moment, limited track use?

And to bother you one last time, what bushings would you suggest at stock ride height? Prefer to keep the cheap stock camber arms for now as well. I'm between stock, or Turner.

Thanks for your time; definitely looking forward to placing an order.

[AussieE46M3]

I thought I had read, and maybe it was specific to non-m's, that if you secure the rear mounts via topside anchoring, then the front mounts won't be able to flex around and tear.

I've seen a few brace manufacturers claim this to however, it's illogical.

There's two moment in action. One about the prop and the other about the wheels. This moment is then broken down into point loads at the subframe mounts.

Looking at it I'd imagine that the rear mounts support the largest portion of the prop shaft torque given the mounts are more eccentric to the axis or rotation. There's still the moment about the wheels axis which the front mounts will be experiencing as well as a portion of the spring force (~1/3) if running a divorced rear setup.

The front mounts admittedly don't seem to be anywhere near as much concern as the rear mounts however, are still a problem. All the M3's I've seen have had plenty of broken spot welds and at least 1 crack beneath the rear seats in addition to the top welds failing.

I recall doing some basic numbers on how tucking a 1" bar beneath the spare wheels well skin impacts the second moment of area and I recall it not being significant and only increased rigidity by a fraction.

I personally perceive the end plates as the most significant part of the puzzle and having a flat plate welded in avoids putting any eccentricity on the plate while having a end plate bolted to the subframe mount and nothing else then introduced bending into the slender bar.

My thinking is a significant reinforcement plate beneath paired with chassis rail plates is the best approach. The bigger plates offer a larger increase in rigidity to the hollow profile much like a slender bar on top and the chassis rail plates stop the panel from being able to pull away from the chassis rail and thus prevents all the subsequent failure patterns.

You can then always add a bolt in brace or additional weld in structure if you want/need more rigidity.

[Jersey_M3]

You may wanna have a look at this option if you don’t want to lose boot space. It looks very well built. If you have Instagram you can go to @weldtechbristol. He is the one who installs them all for the supplier of PSdesigns

http://www.psdesignsglobal.com/_shop/e46---m3/weldtech-bmw-e46-hidden-rear-axle-carrier-panel-reinforcment-brace-kit/

[ZHPizza]

poss

All good I riveted the popped spot welds on the wheel well and made my own brackets to tie the subframe mounts to the chassis rail via rivets and panel bond:



And through bolted the front mounts to eliminate any concerns with the top welds giving out:



Then went all belt and suspenders by adding an x brace too:



Haven't out the side panels back in but I'm happy with how it's shaped up so far:

[poss]

I believe so. I didn't see anything around the mount but there was this plastic wall of sorts about where hotspot #1 is on the diagram.

Unfortunately that may seriously complicate matters and limit your repair options if you have BMW's cavity foam gunk band-aid, as it puts off toxic fumes when heated by welding - so many repairers may refuse to touch it.

I suggest you confirm this before purchasing anything.

That aside, if you put in rail plates you have to cut a section of the boot floor away anyway - so you might as well put a brace in and extend the rear subframe mount bolts up through it while you're there. This is an M3 not some lesser-powered E46 after all. A cavity brace is easily manufactured out of some square section and pipe.

The CMP rear bar is actually 2 bars - one in the cavity and another on top directly between the chassis rails (that protrudes into the boot) to provide maximum possible reinforcement. A single bar between the rail plates is likely more than adequate to prevent RACP cracking, but if you want no compromises rigidity and you don't mind loosing boot space then the CMP bar is the way to go.

[ZHPizza]

I thought I had read, and maybe it was specific to non-m's, that if you secure the rear mounts via topside anchoring, then the front mounts won't be able to flex around and tear.

[dl.m3]

I'd envision it as an extension of the chassis rail so that it drops down onto the hollow section profile the rear two subframe mounts bolt into.

This will provide a direct transfer of stress between the rigid hollow section profile and the chassis rail preventing the rear half of the RACP from pulling down and away from the chassis rail, wheel arch and rearward.

The underside plates also provide a good increase in rigidity to this hollow section so adding the remainder of the topside beam kit would be for the purpose of adding further rigidity over the rear two subframe mounts (eg for big power) and/or to extend forward and include the front two rear subframe mounts.

The vast majority of secondary failures I've seen could have been prevented by the chassis rail to RACP plates being installed with the underside plates however, spot welds are still prone to pop above the front two mounts on coupes.

I plan to add a Mason style rear X brace to my existing Redish plates. Also have 95A poly subframe bushings. Is this going to significantly stress my front 2 subframe mounting points? Car is mostly weekend use and 1-2 track days a year. Not sure if there's a easy way to address the front mounting points without dropping subframe haha, will probably do that eventually though..