E46 Fanatics Forum banner
1 - 20 of 32 Posts

·
Registered
‘99 328i Meergruen Metallic
Joined
·
239 Posts
Discussion Starter · #1 ·
Hey everyone, I have a 99 328i and got a quote to reinforce my subframe for ~$2k. That’s a bit more than i’d like to spend and i’d like to swap all the bushings out on the rear end while it’s off so i’m thinking about attempting it myself. I’ve been looking into DIY’s and came across the Epoxy method. How does this hold up vs welding and is this still a valid repair if it’s already cracking?
 

·
Registered
2000 BMW 323i
Joined
·
79 Posts
I think that rough quote of $2k is to be expected maybe a bit pricey, but that is a big job because you’re dropping the entire rear subframe which is labor intensive. Then having to weld the floorboard that is cracked. If you’re already doing all that work by dropping the rear subframe you might as well do a proper job and re weld the floorboard properly and have the reinforcement plates to suit it.
 

·
Registered
2016 340i xD 6-spd
Joined
·
26,645 Posts
If the epoxy method means the two-part foam treatment, it is not a repair nor 'proper' if the cracks have begun. It's an abatement treatment...but you could diy that yourself after you get the tears welded.

Good luck!
 

·
Registered
‘99 328i Meergruen Metallic
Joined
·
239 Posts
Discussion Starter · #4 ·
Thanks for the answers guys, I’m at 134k and from what i hear the pre-facelifts are more prone to cracking so i’m sure it’s already started. I’ll just save up, get it fixed professionally, and then drop the rear end myself later to do the bushings and what not 👍🏻
 

·
Registered
Joined
·
249 Posts
The epoxy does not solve the problem nor do the plates. There's an updated subframe for post facelift E46s to "address" this issue but literally the entire floor is just too thin. Non M's aren't anywhere near as prone due to have much less power and softer suspension. A chassis reinforcement is the fix like the Vince Bar. If you aren't tearing around corners and flooring it constantly, I wouldn't worry so much. Just when you drop your subframe, grind off the undercoating and check yourself. Some pinch welds are popped at a minimum. Guys are checking their body 5 to 7 years after the plates are welded in and the cracks are back in different spots. I just don't want you wasting your money because just plates are a waste.
 

·
Registered
2000 BMW 323i
Joined
·
79 Posts
Thanks for the answers guys, I’m at 134k and from what i hear the pre-facelifts are more prone to cracking so i’m sure it’s already started. I’ll just save up, get it fixed professionally, and then drop the rear end myself later to do the bushings and what not 👍🏻
Just replace them all in one shot if the subframe is already going to drop to reinforce
 

·
Registered
‘99 328i Meergruen Metallic
Joined
·
239 Posts
Discussion Starter · #8 ·
The epoxy does not solve the problem nor do the plates. There's an updated subframe for post facelift E46s to "address" this issue but literally the entire floor is just too thin. Non M's aren't anywhere near as prone due to have much less power and softer suspension. A chassis reinforcement is the fix like the Vince Bar. If you aren't tearing around corners and flooring it constantly, I wouldn't worry so much. Just when you drop your subframe, grind off the undercoating and check yourself. Some pinch welds are popped at a minimum. Guys are checking their body 5 to 7 years after the plates are welded in and the cracks are back in different spots. I just don't want you wasting your money because just plates are a waste.
I was planning on putting a bar back there after reinforcing. i kinda do enjoy ripping around corners and flooring it lol and i plan on keeping this car for a looooooong time so i’d like to have the peace of mind that it’s been addressed.
 

·
Registered
Joined
·
1,339 Posts
You could epoxy the plates in, foam fill, and use extended bolts or studs to secure the subframe better and avoid shearing. I wouldn’t just count on the plates tho. Cmp auto engineering also makes plates for the top that tie in he frame rail to the racp. Makes no sense not replacing the bushings tho. I think bad bushings are no beuno for the subframe. If you are gonna epoxy the plates, which isn’t recommended, I’d go with this. Oem recommended for certain structural repairs due to accidents. I’m sure it would be okay to glue plates on.

 

·
Registered
‘99 328i Meergruen Metallic
Joined
·
239 Posts
Discussion Starter · #10 ·
You could epoxy the plates in, foam fill, and use extended bolts or studs to secure the subframe better and avoid shearing. I wouldn’t just count on the plates tho. Cmp auto engineering also makes plates for the top that tie in he frame rail to the racp. Makes no sense not replacing the bushings tho. I think bad bushings are no beuno for the subframe. If you are gonna epoxy the plates, which isn’t recommended, I’d go with this. Oem recommended for certain structural repairs due to accidents. I’m sure it would be okay to glue plates on.

Yeah i’d have them swap the subframe bushings when they reinforce it, i’m talking about doing the diff and trailing arm bushings and all that good stuff myself.
 

·
Registered
Joined
·
249 Posts
You can to the bars yourself so you can do it all yourself. I know people will still say do plates but with how physics works, they won't fix anything. Make sure to get a bar that ties in all for subframe mount points as well. You'll be giving up alot of trunk space but this is just the weak spot on the E46. Honestly, I wouldn't worry much with a 328. It's a major problem for M3s. Save up for an M3 and use the 328 as a daily if possible. Then you can invest into a car that will only inceease in value for the most part. That's just my suggestion. I understand the love for an E46. A 325ci got me started on BMWs
 

·
Registered
Joined
·
1,339 Posts
I have the mason bar that connects to a rear shock tower brace. But didn’t install yet. The idea is using longer bolts that go all the way through the trunk into a plate or bar instead of just into the mounts on the racp. You can do the same thing with plates on top and longer studs for way cheaper
 

·
Premium Member
E30M3 Race F10 535 R1150Rt M Coupe
Joined
·
11,277 Posts
IIRC during a rather recent and lengthy thread the only two part foam left (one from the bulletin) all are woefully past the expiration date.
 

·
Registered
Joined
·
1,339 Posts
Very true mrmcar, hard to find anything that can be substituted as well. 3m makes a rigid pillar foam and iirc it is almost as hard as the bmw stuff when cured. Pretty expensive tho and not that easy to find in stock. After I get my plates welded etc. I’m going to try this. I done some tests and it expands very nicely and is hard as hell when it dries. Couldn’t really hurt to try on a already welded subframe, and I’m sure it will at least stiffin the racp more then it is. Lots of jdm guys stiffen their chassis with the 8lb foam. Im assuming the 15lb would be better as it’s more dense. This stuff isn’t the typical spray foam you buy at Home Depot. I’ll make a thread when I do it, but if anyone wants to give it a shot here’s the link. Ps. You can’t weld after since it’s flammable. Hence why I’m doing it after my sub is welded up nice. Gonna also try it on any empty panels to try and stiffen the entire car a bit.

 

·
Registered
2016 340i xD 6-spd
Joined
·
26,645 Posts
Dog...you know to make a sealed cavity first with a softer foam of some sort first? I remember seeing the TIS for it years ago...a few holes to drill and fill...let harden...then fill from the center of those spots with the harder foam. Something like that. :)
 

·
Registered
Joined
·
1,339 Posts
Haha yea, but it seems the point of that is to localize the foam to mount side so the foam doesn’t travel to the other side and not fill it all the way. If filling the entire thing like I plan to, I don’t think it matters but I’ll be the test dummy anyway and let you guys know how it pans out.
 

·
Registered
2005 330i manual transmission performance package
Joined
·
3,967 Posts
I know this isn't very important, but it's inaccurate to call these "foams".
If they were expanding during polymerization, and especially if they were generating gaseous products as a result of the reaction, you can call them foams.

The structural epoxies aren't like this. I have seen both BMW 83190445721 and Lord Fusor 1908. They practically don't change volume during polymerization, and there is no gas trapped inside the hardened material.
 

·
Premium Member
E30M3 Race F10 535 R1150Rt M Coupe
Joined
·
11,277 Posts
Another area of curiosity with any of these foams or fillers is adhesion to the outer walls of the void it's filling.
Sure it fills it up completely (hopefully) and adds strength in the direction of push when decelerating hard, becoming more-or-less uncompressible.
However if the outer surface of the filler has little to no adhesion of the product to the outer walls of the void, one could loose the added strength with respect to shear?

IOW is a special cleaning agent needed and/or an adhesion promoter needed before injection?
 

·
Registered
2005 ZHP
Joined
·
149 Posts
The epoxy does not solve the problem nor do the plates. There's an updated subframe for post facelift E46s to "address" this issue but literally the entire floor is just too thin. Non M's aren't anywhere near as prone due to have much less power and softer suspension. A chassis reinforcement is the fix like the Vince Bar. If you aren't tearing around corners and flooring it constantly, I wouldn't worry so much. Just when you drop your subframe, grind off the undercoating and check yourself. Some pinch welds are popped at a minimum. Guys are checking their body 5 to 7 years after the plates are welded in and the cracks are back in different spots. I just don't want you wasting your money because just plates are a waste.
Exactly. You can just add a chassis bar up top if you don't have any cracking below. Plates are just band-aids.

Very true mrmcar, hard to find anything that can be substituted as well. 3m makes a rigid pillar foam and iirc it is almost as hard as the bmw stuff when cured. Pretty expensive tho and not that easy to find in stock. After I get my plates welded etc. I’m going to try this. I done some tests and it expands very nicely and is hard as hell when it dries. Couldn’t really hurt to try on a already welded subframe, and I’m sure it will at least stiffin the racp more then it is. Lots of jdm guys stiffen their chassis with the 8lb foam. Im assuming the 15lb would be better as it’s more dense. This stuff isn’t the typical spray foam you buy at Home Depot. I’ll make a thread when I do it, but if anyone wants to give it a shot here’s the link. Ps. You can’t weld after since it’s flammable. Hence why I’m doing it after my sub is welded up nice. Gonna also try it on any empty panels to try and stiffen the entire car a bit.

Fyi I've used a lot of the 3m rigid pillar foam in the car (probably a dozen canisters) and it's....ok. It's around 7lb density iirc, so nothing comparable to the concrete that BMW used. I wouldn't expect it to do anything to prevent the RACP issue, but it will help stiffen that cavity a bit.

The simple strategy: Tie the rear mounts into the chassis rail, bolt through the front mounts, weld/plate any cracks that have formed, replace popped spot welds with rivets or seam welding. Done.
 
1 - 20 of 32 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top