Subframe Reinforcement Status Thread

[poth2034]

I worked for bmw years ago and we did the reinforcement plates regardless of cracks or not.

[Mspir3d]

I’m bringing this back again. Mine was reinforced about 5 years ago with maximum psi plates and a bar across the strut towers. They didn’t tie in the front subframe bolts. Today I noticed the floor behind the driver side shock is breaking. I wonder if a Vince bar would help prevent future damage.

[Nuclear Rabbit]

Ouch! It's common for the 3 spot welds that attach the RACP to the wheel arch to fail (I see two popped in yours). Often those panels will be stitch welded together to prevent this type of failure. Vicebar would help too as it gives an alternate load path from the subframe to the chassis.

[Egone]

I’m bringing this back again. Mine was reinforced about 5 years ago with maximum psi plates and a bar across the strut towers. They didn’t tie in the front subframe bolts. Today I noticed the floor behind the driver side shock is breaking. I wonder if a Vince bar would help prevent future damage.

I could see why it continued to crack you need the bar to tie into the rear subframe mounting bolts to spread the load to the chassis rail.

[Arith2]

Don't waste money on plates. They redirect the load to the same failure point, the floor. Get a Vince Bar. That is the fix. These shops just think slapping some thicker metal on works. That's not how it works. The structure needs reinforced. Plates with the bar are probably ok but then you run the risk of putting the stress in an area the chassis wasn't designed to experience load.

[AussieE46M3]

Can you be more precise.

You have personally witnessed post-foam injection subframe failure? With cracks that were larger than the ones that necessitated the injection of foam in the first place? In the same corners where foam was injected? Which corners typically show cracks? Was foam injected into all four corners of these cars or just the left rear as per the BMW TSB?

Sorry for being a few months late to reply. I don't spend much time on the forums these days.

To your first question. Yes. Plenty.

Yes. Some quite terrifying and in places where foam was injected within and beyond.

The places that usually show cracks with or without foam are the same, as welding a crack shut in a stress concentration doesn't do much to prevent it form happening again. 1. Inbound of rear left subframe mount 2. rear left wheel arch spot welds and 3. front right mount.

I do free inspections here in SE QLD Aus and have have seen only 1 E46 (02 auto 320ci with 160k km) of a few dozen (mostly M3's) without any cracks or broken spot welds at all. My M3 was a shocker at 96k km / 60k miles.

If it interest anyone I'm building a cheap little non-M project car up and documenting the process on Youtube and covered exactly these areas if you'd like to see them first hand. The car wasn't very cracked but shows the initial points of interest.

If you find cracks there I'd also have a look behind the rear subframe mounts where the RACP ends as there's 4 spot welds that very often pop and where the chassis rail meets the boot floor running from the back to front mounts. If things get bad enough the rear wheel arch will propagate cracks from the broken spot welds forward alongside the spring perch as per the above post as that's all that's keeping the RACP and chassis together at that point.

Bonus points if you look beneath the back seats along the chassis rail and the furthest forward chassis rail to boot flor spot welds in the corner between the front 2 mount and the spring perch.

I haven't cut into the car to check if they've foamed the front two mounts however, they've filled the rear RACP cavity and it still fails. Foam in this location acts no differently (but much worse) than just underside plates. It's designed to provide localised rigidity to minimise strain in stress concentration and thus prevent fatigue and ongoing cracking. It doesn't correct any of the major design flaws that lead to ongoing cracking (e.g. the rear strucutral hollow section of the RACP does not meet the chassis rail or terminate on anything structural at all).

My advice is if you're wanting a non-intrusive and yet fairly comprehensive reinforcement, install a (good) set of underside reinforcement plates and install a RACP to chassis rail plate. These two combine provide reinforcement to the stress risers in the back half to prevent them from cracking again, increase shear strength on the front mounts to stop the bushing lunging into the chassis causing cracking there and also correct the load path to stop anything forward, backward or outward of the rear two subframe mounts from having issues again.

This unfortunately does not help the front two rear subframe mounts from above so isn't all comprehensive but, gets 90% of the job done on a lean budget and should be sufficient for most E46's (Non-M & M3).

If you want to do more and upgrade to the full topside beam kit for added rigidity and the front mount extension kit to really do the job right the good news is I've updated the design of the topside beam kit to be modular with these plates so that is still an option and gives you time to save up for it if you intend to keep the car long term.

if you track your car regularly, boosted, engine swapped etc I would suggest considering further topside reinforcement. I've seen stock 86kW 318i's with cracks, I suspect you'll need the extra rigidity if you're exerting significant force on the chassis mounts.

If you guys want to see a fairly comprehensive reinforcement with the underside plates + chassis rail plates I mentioned above, I've done a video on that to. The reason more wasn't done to this car is because I've never tried to drift before and don't want to over capitalise on a car that may have a short life.

Last thing I thought I would mention after reading through the comments here, IMO solid subframe bushes are a must on every E46. I've done stock, tried a fully poly PF option and had half the bushes burst or flog out (like many other people) and have ended with stock everything except for solid subframe raising bushes and monoball RTA bushes in my daily driven M3.

The control arms and diff still have their own bushesing so it's no noiser than stock but, I do feel pot holes and reflectors when you hit them yet, it handles infinitely better than poly without any diff whine or clunking.

If you want to read up on it I wrote an article that I posted to the site. https://cmpautoengineering.com/pages...-the-pros-cons

Final note. Poly diff bushes are not an upgrade IMO. Stock in mostly solid stainless steel with only 3.3mm of foam. No noise and next to no movement.

[Tonylauno1]

CMP topside beam and extension can be done from the top without needing to drop the subframe again. So if you had plates previously welded or epoxied, there is some time/work saved. However like I mentioned before, 80% of time is spent on prep - scraping off sound deadening, paint, etc to get a clean area to have clean welds. The amount of prep for topside portion is still non-trivial with everything that has to be cleaned up in trunk and around rear seats.

How do you remove the forward-two-bolt on the rear subframe without removing subframe?
those two bolts are double ended and a nut in the middle.

After you reinforce forward-two-bolt, you need the longer bolt to go right through so you can tighten it from below and above to tie subframe to stronger parts.
Can't reinforce and not use longer bolt.