How would you repair this?

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mopowers

mopowers

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While scraping the undercoating of my 66 Dart, I noticed a crack along one side of one of the front driver's side seat reinforcing plates and the floor was significantly weaker at that point. I popped the plate off and am wondering what the best repair for this would be.

Normally, I'd just weld it up, grind it smooth and tack the plate back on. But since the crack was obviously the result of a work-hardened stress fracture, I'm wondering if I'd be better off replacing some of the sheet metal, or maybe using a different sized reinforing plate so the repair is no longer along the perimeter of the plate.

What do ya'll think? How would you tackle this? The second photo highlights the crack. Thank you!

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Weld. My 66 is like that too in a couple spots. I need to pull the seats and carpet.
 
Weld up the crack and install a larger plate on it. Its under the carpet, nobody will ever know.
 
MoparMike1974 said:
Weld up the crack and install a larger plate on it. Its under the carpet, nobody will ever know.
Click to expand...
Also drill a small hole at each end of the crack before you weld it up. Hopefully that will stop the crack from more flexing
after you repair it. And adding a small strip to your reinforcing plate to make it a little wider to aid in a lasting repair.
Like others have stated it will never be seen when covered with carpet.
 
I'd do like Lee said. I'd use the original plate. Drill a few holes in it and spot weld it right back where it came from.
 
If I had the metal I would make the bracket a 1/4" wider to cover the crack , weld it in, then weld the crack from under to the bracket. Both ways will work.
 
As a professional welded by trade.
Drilling the crack in sheet metal does nothing. It’s sheet metal. Not enough grain structure to carry a crack further. The crack started by loose seat or phat az in the seat rocking back and forth and created the stress. Honestly weld it up with e-70s welding wire (mig machine) and call it a day. If you remove the reinforcement plate and install a larger plate (more surface area) even better.
Nothing to loose sleep over. Easy repair.
 
I would weld and get a helper to hold a dolly against it and flat-hammer the crap out of it to relieve the stress in the weld a bit. And then a slightly bigger plate.
 
Double size of plate,and drill/plug weld two rows of spot welds around plate Will never fail as long as you own it.

imagine a lap joint with one weld along edge. Work it a little and it will break. Having 2 rows of welds and metal is stabilized in such a way that it can no longer flex at weld points.

next time you get near an airplane, look at the rivets. There is 2 rows of rivets holding it together.
 
I don't know if that is factory correct for early a-body or not. I only know these plates in second generation are a good bit larger than what you have there.
 
It was a poor design. Maybe that is why they went to a larger plate on later years. I would remove and replace the plates with larger . As stated you won't see them . And this is one of those instances where "bigger is better". I just confirmed that with my wife.

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Syleng1 said:
As a professional welded by trade.
Drilling the crack in sheet metal does nothing. It’s sheet metal. Not enough grain structure to carry a crack further. The crack started by loose seat or phat az in the seat rocking back and forth and created the stress. Honestly weld it up with e-70s welding wire (mig machine) and call it a day. If you remove the reinforcement plate and install a larger plate (more surface area) even better.
Nothing to loose sleep over. Easy repair.
Click to expand...

or phat az in the seat rocking back and forth and created the stress. due to a 4sp 440 !!!:poke::lol:
 
If you look right above my subframe connector, you can see where I installed a "doubler" for the same reason you are dealing with. I welded the crack first.
Norm

sub frame1.jpg
 
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jazak5 said:
or phat az in the seat rocking back and forth and created the stress. due to a 4sp 440 !!!:poke::lol:
Click to expand...
Mine is cracked and I only have a 4 barrel 273 and a 4 speed. (I do have the phat azz though) :rofl:
 
Agree. You only really stop drill aluminum since that has a weaker grain structure. Steel sheetmetal you weld right over the crack.
 
Thanks guys. Finally had a chance to fix this. I welded the cracks up and enlarged the plate so any stress on the floor pan in the future will be outside of the previous area. Now, I just have to rebuild the transmission hump, then the on to painting the underside.

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mopowers said:
Thanks guys. Finally had a chance to fix this. I welded the cracks up and enlarged the plate so any stress on the floor pan in the future will be outside of the previous area. Now, I just have to rebuild the transmission hump, then the on to painting the underside.

View attachment 1715556772
Click to expand...
Perfect fix. That will last another 50 years!
 
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