How to deal with questionable factory welds

[rftroy]

It seems I got myself a Friday afternoon Challenger.

I replaced the radiator support side pieces to go from a 22 to a 26 inch radiator.  I found that the original driver's side support was only spot welded to the inner fenderwell halfway up, leaving about 8 inches of unattached metal.

When I removed the front driver's floorpan section for rust repair, I found that there were no spotwelds attaching it to the firewall between the left A pillar and the center hump.
Worse than that, yesterday I was sanding the lip of the firewall that was supposed to be welded to the front lip of the floorpan and I found spotweld indentations.  These looked no different than any other spotwelds on the car, except they did not penetrate into the floorpan.  The interface on both sides was smooth and were not welded together.

So now I can't trust any spotwelds on this unibody.
Suggestions?
I don't know of a non-destrucitve way to test spotwelds on an assembled chassis.
It's too late to file a warranty claim.

The two ideas I have so far are:
1.  Use a spotweld cutter to cut through one layer of metal of every interface on the car and plug weld.
2.  Seam weld the chassis.

Anyone seen this level of problem before and have any suggestions?

Thanks,
Robert

[JS29]

Ya they weren't put together vary well it seams! Personally, I would go with option A. 1/8" drill bit and indent the center, than use a blare bit. Weld the new hole shut.   

[jimynick]

Well, unless you're doing a oem resto, I'd do what I did when I found factory FU's and I just seam welded a portion where the non-existent spot welds were supposed to be. Other than non-oem visually, the welds are bigger and stronger. I hear what you say about your car being a "Friday car". In mine, the rt trunk extension was "welded" in a measured and photo'd 3/4" lower than the main trunk floor. The spot welds were half mooned as the panels were so far out of alignment.   

[rftroy]

Yeah.  Unless someone comes up with some really cool, "I never thought of that" type idea, I'll probably do the seam welding once I get the car down onto the frame jig. (And after I weld together the precisely cut pieces for the jig that have been on the garage floor for months.)

I have a hand spot blaster that should work well for the small area in the seam.  And, the idea of drilling all those holes, even with a Blair cutter, makes me tired.

Robert

[JS29]

The factory's spot welded them more than seam welded for a reason.   

[340challconvert]

As I replaced the original trunk floor; welds were sloppy. especially between the trunk floor and trunk extensions.  They were covered with seam sealer; once removed I saw this type of welding. (pic below) A lot of surface welds between the two panels.

On the right side, I drilled some small holes in the new trunk extension and spot welded to the new trunk floor plan for extra strength.
On the left side, I kept the original trunk extension and drilled holes in it to spot weld to the new trunk floor. Reproduced the "sloppy" top welds at the back of the extension near the jack bracket.
Should be strong, but there was no care on keeping the welds looking pretty in some cases.
Also, check out the factory welds on the trunk center bracket.

[340challconvert]

I have to also replace a section of the driver's front floor from the fire wall back. I plan to put in a patch similar to what you have done in that area. I am planning to spot weld the front of the floor pan to the fire wall and at the sill side of the pan,  I plan to then butt weld the back of the patch and right side by the shifter to the original floor just before the front seat mount holes.