How concerned should I be about subframe/floorpan cracks and autocrossing?

[toddztoyz]

I used to autocross a lot growing up. I started out in a 71 Triumph Spitfire and moved up to Formula Fords, then Formula 440, and various street cars. I would really like to get back into it as we have an excellent place to run (has been held in the same place for over 40 years). I have a Convertible ZHP, unfortunately with the 5sp auto and I have been reading up on the weaknesses of the E46 and cracking. I am not looking to get terribly serious, but I will run another set of wheels and tires, and I am upgrading the brakes to stop techs and that will be pretty much it for now. My ZHP sits low enough already as I drag the bottom more than I should so I won't be lowering it.

With all this being said, if I run her once a month or less frequently, do I need to be alarmed about the structural integrity of my E46? If I get real serious again, I may just buy and E30 or an E36 and gut it to build a autocross/track car.

Thanks!

[az3579]

Don't worry about it.

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[toddztoyz]

That's kinda what I was thinking, but I was still a bit concerned as this car means more to me than any other I have!

Mostly I have seen the issue with M3 cars and ones that have not been properly set up for track!

Thanks again!

[Dual]

In recent month's I've run this question past the three BMW-centric shops I trust most near me. I have some mods, as listed in my sig here. Every one said not to be worried. One guy said he'd seen thousands of E36/46 cars including many racers come through the shop and not one had experienced subframe damage.

With luck, you'll hear from the other side here. I know there are owners here who got bit by subframe failure and can tell you about their experiences and opinions.

[fw_fw]

Sometime in 2004 BMW started changing the rear subframe reinforcement by using some structural foam/epoxy inside the rear of our E46s in response to the TSB they issued for the rear subframe failures. With yours being an 06 and an automatic (manual tranny cars are much harder on the rear diff), with the additional floor structure from it being a convertible plus the improved foam reinforced subframe you should be fine.

Some interesting reading here:

http://www.zhpmafia.com/forums/showthread.php?17394-Foam-subframe-reinforcement-production-date-question-technical

[sillieidiot]

It should be fine since auto-x is like low speed. but I would honestly just reinforce it if i were planning to keep the car forever (which it sounds like you are). i'd at least get the front reinforcement plates cause they are cheap.

The issue is widespread on all e46 models. It's just more documented with m3s cause they actually have the money to attempt the repair lol Also they tend to push their car around harder to make the failure noticeable. Then we have all these ZHP guys that think their subframe is bulletproof because it's a later model car. If it didn't cost so much to actually check (proper check requires removal of the subframe and taking the sealant off to look at the subframe mounts), there would be way more reports. A lot of people probably have cracks, it's just not so bad that you can hear the clunk yet.

[Dual]

Sometime in 2004 BMW started changing the rear subframe reinforcement by using some structural foam/epoxy inside the rear of our E46s...I didn't know that. Very good news. I've found a lot of reasons to be happy to own an '06!

[toddztoyz]

Thanks for all the responses to my question and concerns. Like I said, I just want to go out and play a little bit. If I get real serious again I will buy something more purpose built. The car I have was my dad's and was his pride and joy before he passed away back in June. Riding in this car gives me lots of good memories of the time we spent together so that is why this one means more to me than my other toys!

[slater]

lots of info at the bottom. please read (everyone).



Don't worry about it.

why?



In recent month's I've run this question past the three BMW-centric shops I trust most near me. I have some mods, as listed in my sig here. Every one said not to be worried. One guy said he'd seen thousands of E36/46 cars including many racers come through the shop and not one had experienced subframe damage.

the issue is not with the subframe, but with the rear floor cavity. the subframe is where the suspension and diff mount to, and that in turn is mounted to the rear floor of the car. the problem lies in the rear floor cavity. more detail below.

and, i have to assume out of thousands of E46s, that one guy was not inspecting them thoroughly enough.



Sometime in 2004 BMW started changing the rear subframe reinforcement by using some structural foam/epoxy inside the rear of our E46s in response to the TSB they issued for the rear subframe failures. With yours being an 06 and an automatic (manual tranny cars are much harder on the rear diff), with the additional floor structure from it being a convertible plus the improved foam reinforced subframe you should be fine.

Some interesting reading here:

http://www.zhpmafia.com/forums/showthread.php?17394-Foam-subframe-reinforcement-production-date-question-technical

to be clear, starting in 10/04 (although rob's car is 9/04 and his has it, so perhaps it was late september?), BMW started putting a plastic 'filler' piece in the rear floor cavity (which is what is described in that link you posted). it is not structural foam, which is what they prescribed for earlier cars.

the convertible RACP (Rear Axle Carrier Panel), is, i believe, the same as the coupe/sedan/touring, and is susceptible to damage.



It should be fine since auto-x is like low speed. but I would honestly just reinforce it if i were planning to keep the car forever (which it sounds like you are). i'd at least get the front reinforcement plates cause they are cheap.

The issue is widespread on all e46 models. It's just more documented with m3s cause they actually have the money to attempt the repair lol Also they tend to push their car around harder to make the failure noticeable. Then we have all these ZHP guys that think their subframe is bulletproof because it's a later model car. If it didn't cost so much to actually check (proper check requires removal of the subframe and taking the sealant off to look at the subframe mounts), there would be way more reports. A lot of people probably have cracks, it's just not so bad that you can hear the clunk yet.

to the 'low speed' comment - it's not about speed. it's about torque being applied to the RACP. you could drive the car smoothly up to max speed and drive there all day without damaging the RACP.

you are correct about the rest. i'm sure lots more people have cracks/separation than we've heard about.



Thanks for all the responses to my question and concerns. Like I said, I just want to go out and play a little bit. If I get real serious again I will buy something more purpose built. The car I have was my dad's and was his pride and joy before he passed away back in June. Riding in this car gives me lots of good memories of the time we spent together so that is why this one means more to me than my other toys!

you've got an '06, so yours has the factory RACP filler piece. does this make it immune? in my opinion, no, it does not. however it does help.

the main issues are as follows:

1. the RACP (Rear Axle Carrier Panel, aka the rear floor of the car) is too weak - the sheet metal is only 0.75mm thick
2. the subframe mounting points on the RACP are too narrow
3. the subframe mounting points need to be tied into the rear frame rails


the early (pre-2000) E46s tore the RACP at the rear left and front right subframe mounting points. post-2000 cars got an updated RACP design (more spot welds), which was stronger, but not strong enough. post 10/04 cars got the plastic filler piece in the RACP, which definitely helps with preventing twisting of the RACP. the RACP can still crack, at the kink in the RACP just inboard of the left rear mount. this is the most common place on the post-2000 E46s. after that, the RACP separates from the chassis in the left rear wheel well.

how do you fix this 'for good'? in my opinion, 'plates' are not a stand-alone solution. they are a band-aid for the lowest layer of sheet metal only. the spot welds will still pop, and the RACP will still separate from the chassis. you really need to tie the subframe mounting points into the frame rails.

we are really fortunate to have a solution on the horizon - vince in sweden (on m3forum), an ME, has designed and tested his 'VinceBar' which ties the rear subframe mounting points into the frame rails, and ties the front mounting points of the rear subframe more stoutly into the RACP - in fact all 4 mounting points have a bolt-through design. to me, with this approach, the load path for the subframe twisting goes into the frame rails, not on the RACP alone; this solution makes sense. it also installs totally stealth and does not impact usability of the trunk - and for those of us wanting to keep the car forever, it will provide peace of mind.

my car is a 6/04 build car, and i did a thorough inspection last november when i had the entire rear end out for a refresh - no cracks. however, i heard some light creaking upon take off in 1st gear last month, which turned out to be a crack developing in the RACP in the typical first-crack spot. i don't have any separation in the left rear wheel well. my 'VinceBar' (and hopefully 'VincePlates' - they are in development) will be en route from sweden in a couple of weeks. he offers a weld-in kit, and an epoxy and rivet-on kit - which is what i'm doing. i'm going to be doing a separate thread from my build thread on this process.

so, is your car immune? no, but you at least have the factory RACP filler piece. should you keep driving it? yes! should you do regular inspections in the two common areas? absolutely - everyone should.

:cheers

[san]

Vince bar group buy -
Group buy VinceBar ("subframe" fix) - laser cut components

https://r.tapatalk.com/shareLink?url=http%3A%2F%2Fwww%2Em3forum%2Enet%2Fm 3forum%2Fshowthread%2Ephp%3Ft%3D551862&share_tid=551862&share_fid=6222&share_type=t


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[slater]

thanks, san.

yep, that first post has lots of good info in it! vince is a heck of a nice guy, i have gained a lot of knowledge on the RACP issues from speaking with him. i would highly recommends folks here check out the link you posted.

[sillieidiot]

Honestly, he doesn't have to go that crazy and do Vince's fix. From my research and talking to him before. Doing the Mason Engineering brace + Reddish plates should be plenty. His fix is like way above that to go beyond bulletproof. And if you wanted fully bulletproof, you should just wait until Vince comes out with his version of the Mason's X-brace.

[slater]

Honestly, he doesn't have to go that crazy and do Vince's fix. From my research and talking to him before. Doing the Mason Engineering brace + Reddish plates should be plenty. His fix is like way above that to go beyond bulletproof. And if you wanted fully bulletproof, you should just wait until Vince comes out with his version of the Mason's X-brace.

the mason brace does not tie into the frame rails. the redish plates are excellent, but again, they are not addressing main issue.

personally, i don't think anything less than what the VinceBar is achieving (tying into the rear frame rails) is worth doing. plates compliment it, yes - they will reinforce the lowest sheet metal of the RACP - but they are not a stand-alone solution as they do not address the root of the problem.

what is 'crazy' about vince's solution? vince has developed an epoxy- and rivet-on kit - you don't even need to weld anything! anyone who can safely lift the car in the air, and use basic hand tools (dremel, electric drill, rivet gun, etc) can do this. i think it's ingenious.

i'm not a crazy driver; my car has seen zero track time, i'm not drifting it, i never do hard launches. it does see normal brisk acceleration and some high lateral g's, which i'm sure other folks' cars here do as well. so if my RACP can crack - it's only a matter of time until others follow suit.

[toddztoyz]

Wow! Lots of great info here. I really appreciate the in-depth break-down of the what the problem is and how to inspect, what to look for and how to insure you don't have a problem. I hate that this is a major weak link to the E46 because this is such an awesome platform. Makes me wonder if this was the beginning to cost reduction in engineering. I have had several owners of the fifth gen 3 series complain of how cheaply built some of the drive-train pieces are. Of all the previous BMW's I have owned, I would say that they were very over engineered. My E28 was like a brick $#!+ house!

[sillieidiot]

the mason brace does not tie into the frame rails. the redish plates are excellent, but again, they are not addressing main issue.

personally, i don't think anything less than what the VinceBar is achieving (tying into the rear frame rails) is worth doing. plates compliment it, yes - they will reinforce the lowest sheet metal of the RACP - but they are not a stand-alone solution as they do not address the root of the problem.

what is 'crazy' about vince's solution? vince has developed an epoxy- and rivet-on kit - you don't even need to weld anything! anyone who can safely lift the car in the air, and use basic hand tools (dremel, electric drill, rivet gun, etc) can do this. i think it's ingenious.

i'm not a crazy driver; my car has seen zero track time, i'm not drifting it, i never do hard launches. it does see normal brisk acceleration and some high lateral g's, which i'm sure other folks' cars here do as well. so if my RACP can crack - it's only a matter of time until others follow suit.

Mainly just the price. Most people wouldn't even be able to DIY it still though IMO. But in terms of best bang for the buck. Plate + vince's front kit should do a ton already. Obviously not bulletproof, but it's way better than doing nothing.

[Karl Lazlo]

the mason brace does not tie into the frame rails. the redish plates are excellent, but again, they are not addressing main issue.

personally, i don't think anything less than what the VinceBar is achieving (tying into the rear frame rails) is worth doing. plates compliment it, yes - they will reinforce the lowest sheet metal of the RACP - but they are not a stand-alone solution as they do not address the root of the problem.

what is 'crazy' about vince's solution? vince has developed an epoxy- and rivet-on kit - you don't even need to weld anything! anyone who can safely lift the car in the air, and use basic hand tools (dremel, electric drill, rivet gun, etc) can do this. i think it's ingenious.

i'm not a crazy driver; my car has seen zero track time, i'm not drifting it, i never do hard launches. it does see normal brisk acceleration and some high lateral g's, which i'm sure other folks' cars here do as well. so if my RACP can crack - it's only a matter of time until others follow suit.

There should be a like button. Great info, Peter. Thanks!

[slater]

Mainly just the price. Most people wouldn't even be able to DIY it still though IMO.

what's wrong with the price? vince's kit is around $675. that is a HECK of a lot cheaper than repairing a torn floor. it's a bargain, and cheap insurance.

as for the DIY-ability, vince has made it as easy as he can. folks who can't DIY will pay someone to do it. that's how it is with any other trade; if you can't do it, you pay a professional.



But in terms of best bang for the buck. Plate + vince's front kit should do a ton already. Obviously not bulletproof, but it's way better than doing nothing.

i disagree. it's the same as doing nothing... the front kit is not addressing the root of the problem - it's supporting it, but not addressing it. why bother doing anything at all if you're not going to address the root of the problem?

an ounce of prevention is worth a pound of cure!



There should be a like button. Great info, Peter. Thanks!

thanks, man. this forum is about helping each other out, and i feel this is really important.

:cheers

[Sockethead]

The more rigid we make our suspensions ( M3 bushings poly, solid rubber, springs shocks) the more stress will be put on those mounts. All that soft stuff we take out is absorbing a lot of that stress which would otherwise be transferred to the mounts.
I was originally going to just do the reddish mounts eventually but I'm rethinking that.
Thanks for the info!

[sillieidiot]

what's wrong with the price? vince's kit is around $675. that is a HECK of a lot cheaper than repairing a torn floor. it's a bargain, and cheap insurance.

as for the DIY-ability, vince has made it as easy as he can. folks who can't DIY will pay someone to do it. that's how it is with any other trade; if you can't do it, you pay a professional.


I think the math is off. I got like $711 for the epoxy/rivet kit/tool kit (normal version)/shipping. And that is with the current GB pricing @ 10% off. Then labor if you can't install it. So yeah it's a lot. It's basically AT LEAST that much. That's not the total price. You're going to need plates either way if you haven't gotten it already. Need some poly or solid aluminum bushings too.

I guess you could go with the cheapest unassembled stuff. But the labor for welding everything up ends up costing like the same unless you can DIY that too. It's only cheap if you can DIY everything.

Do you even know how much it costs to replace the floor? It costs the same as doing his reinforcement with labor. I would rather do his reinforcement though because that is like a one and done deal.


i disagree. it's the same as doing nothing... the front kit is not addressing the root of the problem - it's supporting it, but not addressing it. why bother doing anything at all if you're not going to address the root of the problem?

an ounce of prevention is worth a pound of cure!

No, it's better than doing nothing :facepalm.

At least that way, you have to option to continue doing the full bar. It's modular. It's like you did like stage 1 (I consider it stage 2 though lol). I'm just saying not everyone could do it all at once. If you can't then do it that way. Sure costs a little more in the end, but you broke it up into pieces you could afford.


Also, for some reason you sound so angry lol

[toddztoyz]

You know, really and truly, this is the repair that BMW should do in a recall! My car new was a grunt over $50k and I would expect better from them. I think the bean counters must have cut some of the cost in the design and engineering of the E46 as this is the only chassis I know of with this problem!

[fw_fw]

You know, really and truly, this is the repair that BMW should do in a recall! My car new was a grunt over $50k and I would expect better from them. I think the bean counters must have cut some of the cost in the design and engineering of the E46 as this is the only chassis I know of with this problem!

They won't.... The cars that BMW made with this type of problem (E36, E36/7, E36/8, E46), some of their best selling worldwide cars. The amount that it would cost to fix all these would be astronomical. Especially since it mostly shows up years after warranty is gone, where they can easily claim abuse.....

[holyc0w]

One wonders how they got some things so right, and others so wrong. :dunno