Subframe weld nut

johnnyfd · Post by **johnnyfd** » 15 May 2025, 15:49

Has anyone dealt with the subframe problem on a p80 chassis in which the receiver for the main subframe bolts has been damaged? This is the passenger side rear mount of the subframe on my 96 850 turbo wagon.
I'm referring to the threaded collar or welded nut, as some people call it, which is mounted inside the unibody and the main subframe bolts thread into.
I'm not referring to the threaded collar itself per se or it's threads being damaged. What has happened in my case is that the unibody sheet metal which the coller is mounted to has corroded and began to tear away from the unibody sheet metal that it is part of.
If this was simply a matter of a welded fix I probably wouldn't be asking, but the mounting of the collar is perplexingly complex in that there are two layers of sheet metal. The lower layer which the collar is actually bonded to and the upper layer which for some strange reason it only passes through without actually being fixed to.
I have gained access from above through a body plug in the passenger front foot well, but a weld from above does not seem possible because the piece of sheet metal which the collar passes through is in the way without any space between that top layer of sheet metal and the coller.
Welding from below is definitely possible but I don't know how it could be done without creating an uneven mounting surface for the bushing and also creating a strong repair.
I'm sorry this is so long-winded but I know that if I do not explain thoroughly without pictures,which I may provide later if I have to, I will receive responses based on not exactly understanding what is going on here because this seems like an obscure situation.

johnnyfd · Post by **johnnyfd** » 15 May 2025, 18:32

It's still not an easy weld job and I don't even have a welder. I imagine a welder would want quite a bit of money to deal with this because it's sort of complicated. Sorry I wrote all that crap before trying to explain what I thought was going on when I had only viewed it from the top because I was afraid if I tried to take the bolt out it would break the remaining sheet metal connection off. Maybe there was a little bit left that I just broke off I don't know. Anyways the bolt is corroded so at least it's good that's getting replaced and not broken while I'm driving it. I'll try to include some pictures of the carnage and hope I get some ideas from everybody. Info2X had the same problem that he posted about 10 years ago. Almost exactly the same issue but he never posted how he dealt with it other than to say he thought he would probably have a friend to come over and weld it from the top and the bottom. I was hoping to get some details from him and sent him a PM but have not heard back. This is a pretty serious issue for this car. I thought I was just checking over some things and was pretty much all set after I replaced the exhaust and the timing belt and took care of a couple of leaks. No such fortune for me!

Post by **Sveedy** » 15 May 2025, 19:04

Seems totally fixable.
You, or someone, just needs to cut out a piece ( maybe 3" x 3" or what ever is necessary ) of the floor around the plug hole. That will give you, or someone, access to weld in a new nut and what ever reinforcing is needed from above. Then weld the piece of floor you cut out back in.
What ever you do labor wise will save you money. Just cutting the access panel out will be a big savings if all a welder has to do is just weld.
If you wanted, once the structural weld of the nut was done, you could buy a wire feed welder for a couple of hundred and weld the panel back in yourself. Not hard to do. Good practice and no one would ever see it.
Then when your door check straps fail you'll be all set

Post by **scot850** » 15 May 2025, 19:14

Just make sure you have the carpet above and the sound deadening peeled back to prevent them catching fire during welding!

Neil.

johnnyfd · Post by **johnnyfd** » 15 May 2025, 19:15

Thanks. My door jam weld is already broken. I sort of like it that way. Makes it easier to open and close the door

.
I agree. This is definitely weldable and it's not the crazy setup I thought it was originally with two layers and the top layer obscuring the job.
What I am still concerned about is finding a way to make sure the nut is not set into place in a way that will throw off the balance or alignment of the subframe at all with all its kinetic stresses and wear out the connection or a different one in short order because the misalignment has created extra stress. I guess that's up to the skill of the welder really, but I'm reluctant to say do whatever it takes to make sure everything is lined up perfectly because that might add up to a huge bill.