CalStang65

Hopefully this is a quick question, but I'm getting used to the fact that they never are:

I've cut out the old floor pan on the passenger side and am preping the new pan for welding. Turns out the shop I'm working at only has can only do TIG welds. What are the pros and cons of tig welding where there were factory spot welds? I figure we can weld the entire frame rail to the floor, weld along the top of the connection to the rocker panel and elsewhere. A guy who knows more about welding thought that drilling out holes to simulate some of the spot welds for the rocker panel connection might be a good idea to avoid the two pieces working themselves apart . . . Another option (although I'd like to avoid it) is to TIG as much as possible and then pay a local welding shop to do the spots. Any thoughts you guys have will be really helpful.

And considering there was not originally a seam along the transmission tunnel, have y'all found it better to have some overlap between the new pan and the old metal extending from the tunnel or did you welding then without overlap? On the one hand, the floor would end up being twice as thick in that overlapping area, but it would also seemingly give the new pan a bit more structrual strength. But I'll go with what you guys think.

Thanks as always!

Cheers,

Alan

109jb

The most common practice wrt the spot welds is to simulate them using a rosette weld. This is as you describe where you drill a hole in one part and make a weld through that hole to the other part. It doesn't matter what welding process you use for this. I've done rosette welds with Oxy/Acetylene, TIG and MIG. Any process will work.

Anywhere you cut something out you want to put the new metal back in to simulate what was there. Already talked about the spot welds. When you cut a piece in two that was originally one piece, like cutting the floor pan along the tunnel, you should weld that line continuously.

Norm Peterson

Preferably with a sound buttweld anywhere that has structural function. Lap welds put a little bending right at the weldand in the adjacent heat-affected zone simply because thetwo pieces of metal are NOT lined up. Fatigue is the main issue, although you're also creating a potential moisture/crud trap. Continuously welding along the "outer" of the bare sheetmetal edges and at least stitching along the inside one would be somewhat better.


Norm

109jb

I missed the part of the question regarding overlap. As Norm said, a butt weld would be best but having an overlap is fine too. The overlap also makes it easier to actually get the pan to fit because you can use sheet netal screws to pull the pieces together before welding. Once welded, remove the screws and weld the holes shut. Like Norm said if you overlap, you can weld one side of the lap continuous and then put some stitch welds on the other side. Lots of cars done without this step though. Use seam sealer wherever the overlap is not welded.

CalStang65

Thanks guys, this is all incredibly helpful. I'm going to pass along all this to the guy whose helping with the welding and if we have more questions, I'll let you know. Seriously though, y'all are life savers.

Cheers!

Alan

CalStang65

Well after four hours of using a metal wheel to clean up the spots that are going to be welded not only can I not feel in my right hand, but I have one more question: When welding, do you guys recommend going from the inside or the outside? Our thought was that a seam on the interior would provide better structrual integrity and water drainage (if any water gets past the sealer we're going to throw on the bottom when we're done), but then again you guys are the experts so I'm sure there's something we haven't thought of.

Thanks.

Norm Peterson

I think I'd rather put the seam on the bottom. Water, especially if it carried a little crud along with it, doesn't always flow out through tight openings very nicely. Tougher to weld without a rotisserie, though.


Norm

Adrenolin

Instead of using screws go buy a box of rivets use these about every 6" to 8" all around, except to the rocker of course. This will securely hold the entire pan in perfect place. Ensure that you have wire wheeled/ground clean all around! I went from the fresh cut up about 4 inches above where the new pan sets. Before placing the new pan in wipe it down well with a good cleaner to make sure there is no grease to mess up your welds. This simply makes for easier and less splatter while welding.

Also, from what I've read and was told you do not need to do any continuous welds on the floor pans. I paid 50 bucks (or was it 80.00.. regardless) on a hole punch that ran off our compressor. Punched a hole every 1 1/4" to 1 1/2" around the entire floor pan which took about 30 seconds. Drilling these is fine also though it'll take much longer. We then set the pan in place and started attaching it by drilling a hole through one of the new punched holes and popped in a rivet. Continue this all along the back, hump side and front as above.. every 6" to 8". Once this was done we started spot welding (or rosette weld) the pan to the rocker. Note that since the rocker is galvanized metal its a bit more difficult to spot to. Its good to have someone behind you with a long bar to apply some pressure anywhere its not tight.

After its all welded in I used a cutting disk (not a grinding disk) on the hand grinder to remove and smoothen out all the spots. Grinding them down takes forever and the cutting disk makes it fairly quick. Beware and alert at all times though. Hand grinders if not kept under control can do serious damage! You know how your hands feel after extended hours holding one lol.

Once welded and smoothed off make sure you have anything you need done regarding welding finished under the car. Then you can paint, POR-15 and seam seal all the edges. Between the seam sealer, POR-15, paint and undercoating it should never get water up in the overlap.

A few things..
[ol][*]Don't butt weld.. use an overlap and spot weld. I left about a 1 1/2" overlap (back, hump side and front toe board) with the pan on top. Attempting to butt weld so there is no seam IMO is simply too much work for a daily driver and will take you a long time to get fitted correctly.[*]Don't do continuous welds. Simply spot weld all around. There are very few places on a Mustang (or any car for that matter) that have continuous welds. The floors don't need them. It is also safer to spot so you don't distort the metal.[*]You will want to stagger the spots. Don't start at 1 corner and work forward (or back). Instead start at say the back corner and do your first spot then jump to the front corner for the second and then back and forth. This also helps from distorting metal.[*]When you come to a hole that has a rivet we simply welding through the center of the rivet and outwards like any other hole. The rivets we used were soft enough they just melted into the spot.[*]When I say spot weld I guess the "correct" term is actually rosette weld. For more info read FAQ #2 here.. and the rest is useful also.
[/ol]There are all kinds of ways to do floor pans. This is just how we did it. Others will of course have their own way. As long as it works, holds and looks good with carpets you'll be happy. Hope this helps.

Adrenolin

Since the edit isn't working....

btw we used a MIG welder for all our spot welding. As for seam sealer seams everyone does it a bit differently and it depends on what and how your treatign the inside and outside of the floors. I'd seal it from the bottom which is then going to be undercoated as well. If your going to POR-15 the inside of the car this will help cover and seal the inside as well as the primer and paint you'll be using inside also.

CalStang65

Well good news. The floors are finally in! What a relief. Thanks for your help! Before doing all the finishing work I want to make sure I'm proceeding correctly. Is the following the proper order?

1. Brush seam seal top and bottom
2. POR-15 all new metal (top and bottom)
3. Prime all metal (top and bottom)
4. Paint all metal (top and bottom)
5. Undercoat bottom

A few questions: First, are all these steps necessary or are some redundant (do I need to paint over POR? Do I need POR? Do I need to prime over the POR? etc.). Second, is it necessary to use the two POR-made prep products POR recommends (Marine Clean & Metal Ready) before applying POR-15--Mustangsunlimited sells both so I have to think they're worth something? Third, do I need to strip the black coating that came with the new floor pans before seam sealing and/or applying POR? Fourth, how clean should the bottom of the car be before starting any of these steps (I have had to do some driving since installing the pans; I know I shouldn't have, please forgive me.) Lastly, how much of each of the products, if they're necessary, am I going to need (pint? quart?).

I'm getting really excited about how this is going to turn out. You guys are amazing. I couldn't do it without you.

Cheers!