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Discussion Starter · #1 ·
I've been reading about E46 rear trailing arm bushings failing and causing stress fractures in the subframe.

E.g. from here

BMW E46 Rear Subframe Reinforcement | BimmerWorld

Now I've heard conflicting reports about which models this affects. Some claim it was fixed in 2001, which means my 2005 car would have had the fix. Some claim it affects M3s and only occasionally 330s.

At this point, I've got the following options

1) Immediate subframe reinforcement and new bushings. The problem is I can't find anyone willing to do the subframe reinforcement. I've heard good things about PowerFlex bushings and the Redish Motorsport subframe reinforcement.
2) It's around 4000 miles to my Inspection II. So I could wait for that. I do know garages that will do an inspection II which means new bushings and a subframe inspection.

One third compromise option would be to do the Inspection II a bit sooner. I do know a place that can do that, they're just not willing to do the welding needed for a subframe reinforcement.

So my questions are

1) Is my 2005 330Ci vulnerable to the issue, or is it pre-2001 M3s and to a lesser extent 330s?
2) If it is what should I do? I've got the radical, and probably radically expensive option 1), or the slacker-ish option 2). Or a compromise option 3)
 

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'02 330i 5-Speed
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The consensus seems to be that BMW quietly implemented the "fix" (subtle redesign of the unibody between the shock towers) sometime in the 2001 model year.

That said, they didn't reinvent the wheel and the geometry that causes the extra stress on the RACP remains, so it's worth reinforcing if you plan to add power and/or keep the car long-term, even if you're crack-free.
 

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'02 330i 5-Speed
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This thread represents the "gold standard" of RACP reinforcement:


I can confidently say he'll never have to worry about it again.
 

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This thread represents the "gold standard" of RACP reinforcement:


I can confidently say he'll never have to worry about it again.
Where can someone even get a VinceBar anymore? What did you wind up doing?
 

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2016 340i xD 6-spd
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The "OE" fix was to weld in a convertible's floor and reinforce between panels with an expanding foam.

You can inspect if you are tearing yourself outside of the rear axle carrier bushings. If not, I'd consider the foam as a mitigation approach, though I believe it's best done after welding on reinforcement plates.
 

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Discussion Starter · #6 ·
I think I'm going to go with option 3) - Inspection II sooner than 4000 miles and get him to check/take pictures of the old and new bushes and the subframe. That way I'll know if I need to worry about the subframe reinforcement.
 

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Oct. 2004 and newer got the internal plastic reinforcement but all cars are subject to this issue - the changes they've implemented at the factory were band-aids at best. IMO if you have cracks and are just driving on the street it you are probably fine with a good plate kit like Redish. If you autox or track your car you want something that ties the subframe mounting hardpoints to the chassis rails, like the vincebar mentioned above, or the kit from CMP Engineering.
 

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I too have a 330ci and the same thought is going through the mind.

211k miles and I don't track but still - for peace of mind.

I am leaning towards putting reinforcement plates using Epoxy. Got no welding skills.
 

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I too have a 330ci and the same thought is going through the mind.

211k miles and I don't track but still - for peace of mind.

I am leaning towards putting reinforcement plates using Epoxy. Got no welding skills.
I would prefer welding over epoxy, as the weak point is not the bottom floor, but the mounts INSIDE the chassis that get loose. Therefore, you have to drill 2 small holes through the chassis (well indicated as there are 2 holes in the reinforcement plates) and weld the actual subframe mount to those plates. Epoxy is just another layer on top of the bottom floor but it doesn't actually help strengthen the mounts inside the chassis. Apologies if this isn't well explained, my English is not perfect.


That being said, I read an article not that long ago (can't find the link anymore) that showed pictures of how the subframe mounts are welded into the chassis, and somewhere 2000-2001 they changed this. So they "upgraded" this. It's still a little sloppy but still better than before.
I have a 2003 and pulled my subframe at 260 000km and there were no cracks at all. Still welded in (read: had my brother weld in) the plates to strengthen it while I was down there anyways.
 

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I wouldn't say so, it was more of a early manual car issue than a later car problem. I have heard of manual E46s being the main suspects for the issue based on the clutch drops being harder on the rear floor from not handling the loading and unloading from the shifts based on what my friend has seen with fixing bmw E46s since they were new. I'd get a PPI before you buy if you wanna see what it looks like from underneath. Hope this helps.
 

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Read this 4 part series by CMP, it explains everything you need to know: Technical

I did a X-Brace on mine since it's more DIY friendly than plates (on top of being a better solution since cracks can come back even after installing plates in some cases).
 

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Read this 4 part series by CMP, it explains everything you need to know: Technical

I did a X-Brace on mine since it's more DIY friendly than plates (on top of being a better solution since cracks can come back even after installing plates in some cases).
I see CMP is sold out of underside reinforcement plates, and they have no email contact. But the Redish plates are available, and Redish have made themselves available for contact.
 

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Discussion Starter · #15 ·
Can Redish recommend a local installer? I was going to give them a call today but I had other stuff I needed to do.
 

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I see CMP is sold out of underside reinforcement plates, and they have no email contact. But the Redish plates are available, and Redish have made themselves available for contact.
Redish is great, their plates are probably the best. CMP has the explanatory articles though so you need to read on their website if you want to fully understand the problem and available solutions.
 

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Convertibles are less likely to suffer due to the extra reinforcement to help keep the body strength without the roof, however they especially M3’s can still suffer. Also depends on how it has or is, being driven - autos only driven in drive when the car moves off effectively in 2nd gear, are going to be less susceptible than one driven in manual mode and accelerated hard off the line, etc.
 

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Convertibles are less likely to suffer due to the extra reinforcement to help keep the body strength without the roof, however they especially M3’s can still suffer. Also depends on how it has or is, being driven - autos only driven in drive when the car moves off effectively in 2nd gear, are going to be less susceptible than one driven in manual mode and accelerated hard off the line, etc.
This approach is more reasonable. If you inspect around each subframe mount and there is no evidence of rust or the crack, then you are safe to continue. Of course you can still reinforce it if you like. But if there is no clear evidence that the condition exists on the car, then no immediate need to repair what you cannot condemn as defective . The rear subframe gets dropped for maintenance at 100k plus, do a closer inspection concurrent with the maintenance.

Kinda like, MS windows blows up a lot. Lets completely tear down all MS windows.
 

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Convertibles are less likely to suffer due to the extra reinforcement to help keep the body strength without the roof, however they especially M3’s can still suffer. Also depends on how it has or is, being driven - autos only driven in drive when the car moves off effectively in 2nd gear, are going to be less susceptible than one driven in manual mode and accelerated hard off the line, etc.
The worst floor tearing/cracking I ever had to deal with was a M3 Cabrio SMG.
But then again my customer 57 going on 17 drove & shifted the car like it was the last lap of Monaco with Lewis Hamilton up in the DRS zone, all the time.

He also managed (how I'll never know) bent all the exhaust valves, with the SMG....WTF. Supposed to be impossible. He did it.
 

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This approach is more reasonable. If you inspect around each subframe mount and there is no evidence of rust or the crack, then you are safe to continue. Of course you can still reinforce it if you like. But if there is no clear evidence that the condition exists on the car, then no immediate need to repair what you cannot condemn as defective . The rear subframe gets dropped for maintenance at 100k plus, do a closer inspection concurrent with the maintenance.
Of course there's no immediate need to repair what isn't broken. But the fact remains that BMW engineers failed to design the rear axle carrier panel for longevity, and the experience of a vast number of owners is that cracks are inevitable:


YMMV, but I'd much rather reinforce the areas on my own terms and timeline rather than driving my high-performance sports sedan around like a grandma paranoid that I'll hear a "death creak" from the rear end if I launch too vigorously.

Kinda like, MS windows blows up a lot. Lets completely tear down all MS windows.
That's only if you decide to abandon the platform entirely. Preventative reinforcement is more like "MS Windows blows up a lot; but I like the OS, so let's tweak the kernel to make it more stable."
 
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