Foam subframe reinforcement - production date question - technical

[AggieBlake]

perhaps a few folks could go in together and amortize the cost of the gun?

Good thinking! If I end up going this route, count me in. I hate buying a tool that doesn't see much use.

Here's another somewhat odd option that's being floated around e46fanatics - you epoxy or weld a 7"x7" plate into the trunk, remove the rear subframe bolt and replace it with a longer bolt that comes all the way through the new plate. Anyone see this or know anything about it? It theoretically makes sense to me since it would distribute the bending loads and reduce warping. It would be WAY cheaper than any other method.

Here's a picture of a really crappy implementation of that idea. Ignore the crappiness and just consider the basic idea.

[AggieBlake]

Here's another picture of the method done by Active Autoworke

http://forum.e46fanatics.com/attachm...6&d=1408159156

[slater]

Good thinking! If I end up going this route, count me in. I hate buying a tool that doesn't see much use.

Here's another somewhat odd option that's being floated around e46fanatics - you epoxy or weld a 7"x7" plate into the trunk, remove the rear subframe bolt and replace it with a longer bolt that comes all the way through the new plate. Anyone see this or know anything about it? It theoretically makes sense to me since it would distribute the bending loads and reduce warping. It would be WAY cheaper than any other method.

Here's a picture of a really crappy implementation of that idea. Ignore the crappiness and just consider the basic idea.

Here's another picture of the method done by Active Autoworke

http://forum.e46fanatics.com/attachm...6&d=1408159156

my problem with that is that the 'drawing' is not accurate. there is space between the top of the subframe bolt carrier/receiver and the uppermost trunk floor sheetmetal. you would end up collapsing the trunk floor onto said carrier/receiver.

filling, to me, makes the most sense - it's non-destructive (so to speak - nothing changes in vehicle operation or appearance), it's easier to do, and it's cheaper. and from a technical perspective it makes the most sense to address the issue at hand - to me, anyway.

i filled.

[Sockethead]

my problem with that is that the 'drawing' is not accurate. there is space between the top of the subframe bolt carrier/receiver and the uppermost trunk floor sheetmetal. you would end up collapsing the trunk floor onto said carrier/receiver.

filling, to me, makes the most sense - it's non-destructive (so to speak - nothing changes in vehicle operation or appearance), it's easier to do, and it's cheaper. and from a technical perspective it makes the most sense to address the issue at hand - to me, anyway.

i filled.

I agree. The bolt/plate would have to terminate on top of the second layer... easy enough to do by cutting a hole in the top layer to get access. Most welding repair kits have you cutting an access hole there and adding welds to that area as the spot welds between the second layer and bracket are what fails.... the bolt would take the place of the welds and you could epoxy a plate over the hole... That method would require no welding at all but you are still cutting into the structure...

[AggieBlake]

Yep, I see that now. You're both absolutely right. This would be pointless without removing the upper sheetmetal, meaning that this method requires cutting, which I'm not super excited to do. I'm surprised the Active Autowerke drawing is wrong. Those guys typically know their stuff.

One other issue with this method: if it is mounted on the middle sheetmetal, it won't actually have much contact area since that sheetmetal has divets in the pictures I've seen. It's not flat like the top sheetmetal. So another reason to go with the epoxy method. Just wish BMW would write me back with a clarification

[slater]

Yep, I see that now. You're both absolutely right. This would be pointless without removing the upper sheetmetal, meaning that this method requires cutting, which I'm not super excited to do. I'm surprised the Active Autowerke drawing is wrong. Those guys typically know their stuff.

i would be surprised if that was their actual 'drawing' - looks like someone made it in MS Paint. another interesting thing is that they have zero information about this on their website. so who knows where it came from?

One other issue with this method: if it is mounted on the middle sheetmetal, it won't actually have much contact area since that sheetmetal has divets in the pictures I've seen. It's not flat like the top sheetmetal. So another reason to go with the epoxy method. Just wish BMW would write me back with a clarification

yep, exactly.

also, you should heavily consider replacing your subframe mounts with units like the AKG poly ones - they have a flat face (and harder durometer than powerflex, if i remember correctly), which helps distribute subframe load on the rear floor a lot better than the stock ones (which just concentrate it on a very small area surrounding the bolt). i used these... fitment was very good. there's a pic or two here in my build thread: http://www.zhpmafia.com/forums/showt...844#post459844

[AggieBlake]

Ok, I finally got a chance to put a borescope down the hole and take some video for you guys. The video quality's not great (had to improvise with my iPhone b/c the scope had no record capability). But it did the job. You can clearly see the plastic piece that's been added. It's substantial and it is epoxied in place. There is virtually no room for liquid epoxy to be injected into the driver's side cavity unless the viscosity were very low, which I doubt to be the case. There is no such plastic piece on the passenger side, meaning it would be easy to do the epoxy reinforcement on that side.

Here's a link to the video...
https://dl.dropboxusercontent.com/u/...0Video%202.mov

Having studied this, I am now 95% sure that the purpose of the piece is to reinforce the subframe and prevent cracking. Keep in mind that the piece was added into production 5 years before BMW released the epoxy repair protocol (in 2009). So it can't be a dam to make the epoxy method easier (contra Reddish) b/c no one was injecting epoxy into these cars back in '04. Instead, I believe BMW added this piece to stiffen the floor (a metal/plastic/metal composite sandwich) because they were hearing about more failures in earlier cars. Years later, as the failure rates of older cars increased, BMW began to look for a way to mimic the effect of the plastic piece in existing cars (obviously you can't add the plastic piece in to a chassis that's already welded together). The epoxy was the best available option. With the expanding foam barriers in place, you are effectively creating a plastic-like block between the sheetmetal layers, creating a metal/epoxy/metal composite sandwich. This would explain why they did not allow their techs to do the epoxy method on cars produced after 10/2004 - the plastic piece has the same benefit as the epoxy. If the subframe still failed, there was nothing left to do but replace the whole thing. This would also explain the much lower rate of failure of post-10/2004 cars. I only found 1 instance online of a post 10/2004 failure that I could verify, and even then there were no pictures or details to explain where it failed.

Summary: for e46's produced after 10/2004 (or thereabouts) that include the plastic block reinforcement in the chassis floor, there appears to be no way to fill the driver's side cavity with epoxy and no need to do so. That location has already been strengthened. However, it's still worthwhile to reinforce the passenger side mount with epoxy injection on a car that will see hard driving, especially one on a stiffer aftermarket suspension. That's what I plan to do at some point in the near future.

[Vas]

I need to check both of my vehicles

[Johnmadd]

Great thread, I enjoy the your research. I am now Paranoid... thanks bro.

[slater]

Ok, I finally got a chance to put a borescope down the hole and take some video for you guys. The video quality's not great (had to improvise with my iPhone b/c the scope had no record capability). But it did the job. You can clearly see the plastic piece that's been added. It's substantial and it is epoxied in place. There is virtually no room for liquid epoxy to be injected into the driver's side cavity unless the viscosity were very low, which I doubt to be the case. There is no such plastic piece on the passenger side, meaning it would be easy to do the epoxy reinforcement on that side.

Here's a link to the video...
https://dl.dropboxusercontent.com/u/...0Video%202.mov

Having studied this, I am now 95% sure that the purpose of the piece is to reinforce the subframe and prevent cracking. Keep in mind that the piece was added into production 5 years before BMW released the epoxy repair protocol (in 2009). So it can't be a dam to make the epoxy method easier (contra Reddish) b/c no one was injecting epoxy into these cars back in '04. Instead, I believe BMW added this piece to stiffen the floor (a metal/plastic/metal composite sandwich) because they were hearing about more failures in earlier cars. Years later, as the failure rates of older cars increased, BMW began to look for a way to mimic the effect of the plastic piece in existing cars (obviously you can't add the plastic piece in to a chassis that's already welded together). The epoxy was the best available option. With the expanding foam barriers in place, you are effectively creating a plastic-like block between the sheetmetal layers, creating a metal/epoxy/metal composite sandwich. This would explain why they did not allow their techs to do the epoxy method on cars produced after 10/2004 - the plastic piece has the same benefit as the epoxy. If the subframe still failed, there was nothing left to do but replace the whole thing. This would also explain the much lower rate of failure of post-10/2004 cars. I only found 1 instance online of a post 10/2004 failure that I could verify, and even then there were no pictures or details to explain where it failed.

Summary: for e46's produced after 10/2004 (or thereabouts) that include the plastic block reinforcement in the chassis floor, there appears to be no way to fill the driver's side cavity with epoxy and no need to do so. That location has already been strengthened. However, it's still worthwhile to reinforce the passenger side mount with epoxy injection on a car that will see hard driving, especially one on a stiffer aftermarket suspension. That's what I plan to do at some point in the near future.

awesome, awesome work blake! thanks for taking the time to scope (ha) that out, and post the video. i definitely agree, there is some room to fill the cavity on the driver's side - i would do that and also the passenger side.

cool stuff. mine was produced in 6/04 and did not have the plastic piece.

I need to check both of my vehicles

LOL. what's the build date on your 2004?

Great thread, I enjoy the your research. I am now Paranoid... thanks bro.

ha!! if you have no cracks, filling is easy. cheap insurance. also, i highly recommend the AKG subframe mounts - insurance and better feel/feedback.