"I wouldn't trust a pop rivited floor pan to hold my seat"

I would not either... and of course the steel to steel rule should be followed for several reasons...

typically one would use the air tool which will cut nice holes fast along the edge of the piece then turn that tool over and use it to flange the larger metal so the edge would be flush.... then the piece would be placed where you wanted it... and 1/8th inch holes drilled...and pop rivets used to hold it in place... or Clecos if you did not want to leave any rivets...... then at the places where the holes were made along the edge you would plug weld.
I believe I have posted pictures of that tool.

If you could find an aftermarket floor pan or rust free used one it isn't too bad a job to weld one in. Not that I really have anything against pop rivets, I've used them plenty, but a MIG welder is a common tool these days and there are people out there that can be reasonable in doing work. I have my own and though I'm not much of a welder, I can do what I need. There's no real reason to rush into fixing it, but it's never a bad time to start exploring your options.

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'82 300SD - 361K mi - "Blue"

"Good judgement comes from experience. Experience comes from bad judgement."

listen, look, .........and duck.

Ok, I stand corrected there are structural pop-rivets, but you must make the distinction between structural and non-structural rivets. Most structural rivets are solid rivets and are hammered in place. Structural pop rivets are not the norm and most pop-rivets are not structural. Make sure you get structural rivets for structural work.

As noted aircraft are largely riveted, but mostly not with pop rivets, once again with solid structural rivets that are hammered in place.

If you look at things built in the early part of the 1900's you will see that everything was riveted, pressure vessels, steel ships, bridges. Those rivets are basically hammered into place. Big old ships had literally millions of rivets. As soon as welding was practical it replaced most of this type of riveting.

I use pop rivets, I like pop rivets, but keep them in their place. That place is not where they are subject to stress and expected to hold, unless you are sure you have structural rivets.

Seriously folks, I hope you can appreciate the forces involved in car wrecks and don't take chances.

While we are on this subject of strength....
I hope people will not be visualizing BUTT WELDING new metal to old metal as a strong way to put these floor pans in...
Structural strength in an accident is very important...
and the method which I described... which gives an overlap of the two metals and combinations of riveting to hold in place.....and plug welding ... can make a very strong pan.

guys, just an update.

no body shop in town wants the job as i described it to them over the phone. they said it would take up too much rack time. go figure.

next, i took out the mats and found no holes. but what are these rubber stoppers for on the floor plan? should they be removed?

i then called my local indy and described the problem. he said there is really nothing practical i can do. live with it he said. it is an old car. fine with me for now since i can't afford it anyway.

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Jennifer
90 350sdl

That is the way I was taught, overlap, flange, plug weld. Look at the spot welds in a body to see an example.

There is a good weld-through coating you can spray on for rust prevention between the overlapped panels, marketed by Pittsburg Paint.

On really large patches you can stitch weld with welds about an inch long spaced a few inches apart. I would have to look-up details before I did it.

There are textbooks for auto body repair that are excellent references. Check the library or book store. If you ever see one cheap, used, grab it.

"next, i took out the mats and found no holes. but what are these rubber stoppers for on the floor plan? should they be removed?"

Jen-

When you say this , I hope you are looking carefully at the asphalt-based sound proofing between the carpet and the floor. If you suspect any corrosion under this at all you should peel some of it back and make sure you have solid steel underneath. When water gets under this layer, it eventually rots the steel and it may well still look good from above.

The rubber stoppers , I believe , are drains that go through the floor. Leave them.

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80 300SD (129k mi) 82 240D stick (193k mi)77 240D auto - stick to be (153k mi) 85 380SL (145k mi) 89 BMW 535i 82 Diesel Rabbit Pickup (374k mi) 91 Jetta IDI Diesel (155k mi) 81 VW Rabbit Convertible Diesel 70 Triumph Spitfire Mk III (63kmi)66 Triumph TR4a IRS (90k mi)67 Ford F-100 (??)