Broken Unibody Seat Weldnut

Well the worst answer would be to drill all the way through and put a bolt in its place, with a hefty washer to distribute the load across the floor pan in case of an accident.

I'm sure there's a more elegant solution, too. Can you fish a nut down in there? If you can do that, you can thread some allthread into it then torque another nut down from above, pinching the thread with a vise grip.
 
The issue is if any fix is OEM equivalent to stave off liability problems in the event of an accident.
 
So if you can't see the nut on the underside, then where is the nut at? In an enclosed area of the uni body frame?
Fire can be an issue when welding on an assembled car so be careful. If the nut is hidden, I'd cut a small window around the nut, and remove it and make the patch with a new nut, but like others say a larger plate will be best to distribute the load. Where is a photo of it?
 
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There’s an obvious overlooked issue. HOW did you possibly do this by hand? There must be damage or another flaw going on. Seat nuts IME have been very securely welded to thick metal. Is there other damage, tearing, rust….?
 
There’s an obvious overlooked issue. HOW did you possibly do this by hand? There must be damage or another flaw going on. Seat nuts IME have been very securely welded to thick metal. Is there other damage, tearing, rust….?
How? This has happened before on a Lexus vehicle. First time was an LS400. I remove the seat bolts with either a ratcheting box wrench or impact wrench. No rust, no crashes, no damage. All Florida cars. I'm never removing another seat again to clean underneath.
 
How? This has happened before on a Lexus vehicle. First time was an LS400. I remove the seat bolts with either a ratcheting box wrench or impact wrench. No rust, no crashes, no damage. All Florida cars. I'm never removing another seat again to clean underneath.
Ahhh. I wouldn’t say to never do it again, I might just advice turning these by hand. You can’t feel what’s going on with an impact, and it’s working against reinforced sheet metal in some cases. I’d suggest using hand tools to at least break it free as they will communicate to you if something isn’t right.

I’ve used an electric impact a few times on my truck, which is a rust free southern car, but my electric is also weak and probably doesn’t eek out more than 45 ft/lbs, about half its rating.
 
+1. Easiest solution. As strong as OEM? No. But what else are you going to do? Welding seems a bit involved.
I'm debating whether a rivnut would be acceptable or if I should drill through the floorpan and nut/bolt the seat in place.
 
I'm debating whether a rivnut would be acceptable or if I should drill through the floorpan and nut/bolt the seat in place.
If you look at the surface area a rivnut captures, it's negligible under considerable (subjective, I realize) load.

They're super handy for light duty stuff but not really intended for occupant seats.

It just depends on how OCD you are and the level of risk you're willing to assume.

If you were near me I'd weld in a patch for free just so you can sleep at night (cue all the YoU'LL GEt SuEd!!!!! fearmongers)
 
If you look at the surface area a rivnut captures, it's negligible under considerable (subjective, I realize) load.

They're super handy for light duty stuff but not really intended for occupant seats.

It just depends on how OCD you are and the level of risk you're willing to assume.

If you were near me I'd weld in a patch for free just so you can sleep at night (cue all the YoU'LL GEt SuEd!!!!! fearmongers)
Weld in a patch from above or below?
 
Weld in a patch from above or below?
I thought you didn't have access from below? I wouldn't run a bolt thru an air gap unless you sleeve it so you can torque it gutentight and have nothing collapse.

That said, IF you could do that you could just weld your sleeve at top (inside) and bottom (underside) and be done. Two round welds vs a rectangular weld inside.
 
I thought you didn't have access from below? I wouldn't run a bolt thru an air gap unless you sleeve it so you can torque it gutentight and have nothing collapse.

That said, IF you could do that you could just weld your sleeve at top (inside) and bottom (underside) and be done. Two round welds vs a rectangular weld inside.
I can't find where the original weldnuts are from below, but, I can almost certainly drill a hole all the way through whatever structures there are between the top of the seat and the very bottom of the car.

If I weld in a patch from above would it be advisable to weld in a patch on the adjacent bolt so that the seat is at least level?
 
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