Project 3 from ogorir: floorpan/firewall rust repair

This is a '65 saab 96 that I cleaned up for the boss to give to one of his son-in-laws. this spot is rusty on ALL of them. ALL.


what was there:
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with bottom 2.5" of the (rusty) firewall cut away:
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a section that needed to be replaced in the inner fender well (and the swiss cheese that came out):
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the hole I ended up with after cutting out all the rusty bits and the main patch 'panel' (yes, it's basically just flat 19ga.)
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you can see that I plug welded everything, used the I-MIG, of course. probably around 16.5v, and '185' on the wirespeed, but that doesn't actually mean anything on anyone elses unit. I think that translates to about 375ipm, .030" ER70S6.

(cont'd next post due to pic count limit)

Wow, that is some rust. Did you leave the floor flat or did you bend it to match the floor pattern (corrugated type bends to stiffen up the floor pan)?

patch panel in:
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you can see the burn-through spots where I welded the supports on the underside (I thought I had a pic of this, but I don't). basically, I folded up some short sections that match the ribs stamped in the floor pan and welded them on after it was in the car. I did this for 2 reasons: A) our brake sucks. B) it's arguably stronger than the original floor pan.

I had to make one section bolt in, as the brake lines are supposed to run inside the car in the bottom of one of the ribs. I welded nuts to the support channel so once you get it up there, you can tighten it all from one side.


this is the setup I used to make that radiused hole. it's 2 big 1" drive sockets, one just fits inside the other. I drilled a whole with a step bit, then used a carbide burr to enlarge it to the diameter of the small end of the small socket. this gave the socket a bit of a pilot to work with. I beat the little socket through and it left a nicely radiused corner. because my hole wasn't round, the edge was a little screwy, so I took a flap wheel and ground it flat.

the beads were put in with a bead roller, the hole I beat around a dolly clamped in the vise. this bit took some work to make the hole the right size for the brake lines to go through the floor.
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this last one is (almost) everything welded in, caulked and sprayed black. I was hoping the flange I made to support the corner of the flat panel was going to cover the hole that's till left, but I ended up having to make a piece and weld it in. in hindsight, I'dve made it part of the big flat panel. I think I was trying to use a drop from another panel to make that flat bit, which is probably why I cut it there in the first place.
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this is also a bit of an experiment. I used standard outdoor latex house caulk as seam sealer. we'll see how it performs over the next few years.

This is all covered in foil lined dynamat now.

I think this took 4 days start to finish to put in the patch. it took 2 weeks to rub/wax/throw some rattle lacquer on some thin spots, fix this rust, paint some POR-15 on a bunch of other minor rust, put in the dynamat, and run brake lines.

Quote:

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Originally Posted by DVA

Wow, that is some rust. Did you leave the floor flat or did you bend it to match the floor pattern (corrugated type bends to stiffen up the floor pan)?

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and this was a pretty clean one. to their credit, this is really the only spot they really rust out in. the engine compartment side can be pretty bad, too, though. the bottoms of the doors also get pretty rough, and the corners of the cowl just ahead of the door and behind the hood are all rotted out. that cavity is open to the fresh air intake from the inside and there's no drain until it rusts a hole through it.

yes and no, I folded up some sections that I welded underneath to match up with the existing floor and stiffen it up. unfortunately I don't have any pictures of the underside.

I like your flanged lightening hole. Very clever and very nice result, for just having a couple big sockets laying around. Nice work!

Where do you source your metal for something like this? Do you have a preference for using galvanized or other coated metal in any circumstance, or do you prefer uncoated? Are you finicky on what thickness material you use? Cheers!

I used 18ga CRS for this, if I remember right. I got 10 sheets of what was supposed to be 20ga CRS, but is actually 21ga, from one of the local steel suppliers, but I had to order it in (hence 10 sheets).

I only used cold rolled steel for patch panels. you could probably use galvanized for structural stuff if you could find it thick enough, but you'd wear it all off if you were forming a compound curve, ect. also, cold rolled is generally better steel stock, easier to form, ect.

as far as absolute thickness, I typically replace sheetmetal with what was there originally, unless i have reason to do otherwise. 20ga is really easy to work with but is still strong enough for most things, provided you put a compound curve or some stamping in it, 18ga you can get away with wider flat areas. 22ga is fairly useless in mild. anything thicker than 18ga is bracket material, bumpers, or a scatter shield.

I'm hoping in the next year we'll be making a few equipment purchases so I can actually start making real panels. the little e-wheel we have is a POS, as is the brake (non finger model). I still need to build tom's (acourtjester) bead roller plans. having a powered roller is a huge advantage. right now, though, I just have to make due with what I've got. fortunately I'm doing mostly mechanical right now.