That's pretty much the only non 323/328/m3 car I've seen with cracking. wow. I said a long time ago time will be the factor for 325/330 cars to start showing this.

JB weld (or similar epoxy) IS the preferred method for attaching plates.

however for a proper repair, i'd recommend a whole new rear floor fresh from BMW (brand new part) as the aged spot welds and fatigued metal are really the culprit here. anything short of that is just a temporary solution (which could be fine if you aren't keeping the car long)

 

Do you have a part number for that and/or does BMW even sell that part?

 

Thanks mango one more time for you knowledge, i will start looking into the parts see if i can do that job (I work alone) and do it the best way possible since I'm planing to keep her, My coolant system is "MANGO PROOF", thanks to you.

 

Yup.

To reinforce my plate comment (no pun intended), remember the job of the plates is simply to distribute load and to "beef" up that part of the sheet metal (make it more resistance to flexing)

So welding isn't necessary. And could even be detrimental. Welding the perimeter of the plates still leaves an air gap whereas epoxy seals the plate to the car and you have 100% contact throughout. Now will welding work? sure. But epoxy is not only easier, it's more effective.

 

sounds good, epoxy it self will be then.

 

I would not use JB Weld, if doing this do it right with the industrial strength epoxy BMW suggests.

i love JB Weld, but until you find it’s specs are close enough to the approved epoxy i would not waste my time.

also those appear to be stress fractures, be surprised if they are allowing a clunk sound. that’s usually a full breach of the metal flexing in and out. but the internal threaded block for the bolt could be loose inside the rear floor panel. those spot welds give and then it allows movement which cracks the floor.

 

good point, i normally saw a lot of threads with people using JB Weld, and had no issues at all, thats why i decided to doit as well with it, will inspect the bolts and also cut the upper panel and inspect the plate on the top.

 

Use a structural adhesive like 3M 08115. Also fill the cavities with foam.

 

+1.
Either that, or 3M DP420NS:
https://www.amazon.com/3M-Scotch-Weld-39285-Adhesive-DP420NS/dp/B071LQJL2C/ref=sr_1_1?ie=UTF8&qid=1522993403&sr=8-1&keywords=3m+dp420ns#customerReviews
Get the appropriate size applicator gun as well.

 

There's a non-weld kit available - of course it is more involving than just dropping the subframe and gluing the plates
http://www.m3forum.net/m3forum/showthread.php?t=546116

 

i saw that reinforcement bar in another thread, really cool, mines its a 325i which they are rare to break, but its stressed, and the CLUNK noise already found out where it came from:
my RTA bushings are really bad, and the RTA rear ball join the one that connect to the under spring plate are horrible, will change those as well, so this project its extending for more time. i was planing finishing it up this weekend, but new part needed to be purchase and this make me wait more time.
any preferred web site to upload pics and post in here, without using my non pay membership space?

 

Imgbb.com is free
Google drive is free
Imgur.com

 

The best method is new floor
bmw foam cavity
custom plates expoxied on
careful non-hooligan driving

even with all the above, the inherent design SUCKS and it WILL fail again.

this is why e39/e90 and every car from after that uses WIDE footprint subframes.

For reference, the rear subframe in my Lexus goes from extreme edge to edge using MASSIVE mounts and heavily reinforced mounting areas. no way that sucker is failing.

 

https://www.ecstuning.com/b-genuine-bmw-parts/rear-sub-frame-support-panel/41117000246/

this is what you talking about?
if so i will fix this the best way possible.

 

got 2 kit of the 3M 8115, from local shop them have them in stock, already cleaned everything and glue they plate with the epoxy, see tomorrow how it end will post some pics, also the shop adv me that they see other customers cars with JB Weld as well, and no issue with the sub. lets see how mines ends.

 

lotta experience and knowledge here impressive. I replaced my subframe couple years back. My subframe separation was done by the dealer several years ago covered under the class action suit i got lucky. ebay sells used refurb subframes from california with brand new bushings pressed in for 100 bucks. If your subframe is rusted out i highly recommend replacing it especially if you have worn bushings. Kudos to all you guys DIY this. You can leave the trailing arms in the car and take the bolts out and pull the subframe out without removing the trailing arms. first remove the diff. i thought that was alot easier. also you should replace the hard brake line behind the subframe if it's worn/rusted. POR15 rust treatment is perfect here too if you have any rust issues. It's a ton of work but you should take care of everything in there if the subframe is dropped/out. I did the emergency brake lines too they were shot ECS tuning has good kit for that. I soaked all the nuts and bolts in apple cider vinegar to rust treat for a few days just shake it up once a day to mix it. then i soak hardware in wd40 for a couple days. comes out really nice.

 

my car doesnt have any rust, its clean, never been on snow, im from florida and move to las vegas 8 months back, also i took out the RTA because will be replacing those bushings too.
my plates are glue and ready to start mounting everything back.

now i have a question:
what about solid (like hard solid plastic or aluminum) subframe bushing?
i know this been cover before, but no one put the experience of it, is it bad for the car or good? will it break my floor? will you do it? any one with them on now?

 

my car doesnt have any rust, its clean, never been on snow, im from florida and move to las vegas 8 months back, also i took out the RTA because will be replacing those bushings too.
my plates are glue and ready to start mounting everything back.

now i have a question:
what about solid (like hard solid plastic or aluminum) subframe bushing?
i know this been cover before, but no one put the experience of it, is it bad for the car or good? will it break my floor? will you do it? any one with them on now?

solid bushings in the subframe-to-floor cause a lot more stress to the mounting area. i recall several people in the past saying it caused cracks in their E46 non-M RACP. there are few threads on it if you do a Search. i would not go aluminum or delrin unless you plan to track and take car apart and fix often.

 

got it that's what i needed to know thanks, i use the word "glue", because i don't know how to refer to the process that is complete, glue or weld. thanks for the info about the solids mount, wont be using them, i normally work from home and i could say i put around 2k miles on the car a year now, also have 2 more vehicles that i use as well, so its not something that she gets a lot of use, but i love the ride every time on her.
I'm guessing no "Polyurethane" either right? i need to replace them because mines are kind of 5-10 some crack on them.

 

there’s a shop in the UK that does a lot of subframe floor repairs and swears by the power flex urethane bushings. says the top surface area is better planted against the metal and spot welds of the factory floor. since you’ll have plates this won’t be a factor. but the Power Flex are easier to install and the street versions are said to be fine for stress levels. if your bushings are good they make an insert that caps and inserts into the gaps of the factory bushing. this maybe the easiest upgrade for your situation. :dunno:

 

got it, well already order the oem ones, got them on a really good deal, i know they are super hard to put, but lets see how it goes.

 

i***8217;m sure new fresh mounts will feel better than old worn out ones. you***8217;ll be good

 

yes definitely this was supposed to be a weekend project, and its more than a 2 week project, well im sure i will love the result, and there will be no more weird sound on the back.

 

This is probably only a temporary solution at best. The cracking isn't the subframe/RACP biggest issue; the panel separation is. Unless you engineer a solution that will stop the panel from flexing, you'll just find the next weakest point.

Look into a vincebar and use the right epoxy. That's the only style of solution that will last the lifetime of the car.

 

OEM or M3 bushings in the entire car i would say. dont recommend any "POLY"/hard stuff. unless you race the car maybe. dont recommend any of those metal covers that cover any bushings. long term i think its bad for the car plus creates or vibrations for less comfortable ride.

 

Forgive the thread jack.
I'll be doing subframe plates this summer, as well as an m3 subframe.
I purchased a full rear ens bushing kit with the originally planned non-m subframe.
Are the non-m subframe bushings compatible with the m subframe?

Sent from my tractor.

 

Hows it holding up now? any changes/degradation?