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I'm preparing to weld patches to fix the holes in the floor, and I see these circular rubber plugs. There is surface rust around the plugs, and I'm thinking of removing the plugs and welding over them. Does that sound like a good idea? This is my first time welding. I'm guessing the plugs had some purpose at the factory, perhaps to drain some type of chemical liquid. There are plugs in the rear floor as well.

I'm planning to weld the patches, wire brush the floors to bare metal, then use the Por-15 products to paint the floors.





The floor near the central tunnel has quite a bit of pitting. I'd rather not cut too much out if I don't have to, especially since that hole is about the size of a quarter. But maybe the metal is so thin that I have no other option but to cut a couple square feet out. What do you think?

 

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Just a small disclosure - I'm not a pro, I'm pretty much a shadetree hack - this is just what I've learned about rust over the years by restoring several rusty old cars from the snow and salt belt with my dad.

I'm preparing to weld on my Saab as well, in the trunk area. Here's my plan: I'm leaving the rubber plugs in - usually they are there for rain water or the snow and other crap you drag in on your feet. If you look at replacement floor pans from other cars (Mustangs, Camaros, etc.), these holes are always retained and they sell replacement rubber plugs. FWIW, I plan to practice a bit on thin sheet metal (MIG + gas) so I can minimize the risk of blow through when I actually go to weld - I expect the metal to be very thin around the rusted areas on my car. I have not welded on a car in 10y, so it's like starting from scratch, but I do remember the surrounding areas are very tough because they are often quite thin.

Once the patches are in, I plan hit any remaining rust with a converter, an encapsulator and then a chassis paint - I'm using the Eastwood products for this. However, I don't think you ever really get rid of the rust - you basically just slow it down and hope it doesn't bubble up a few inches away in a few years.

Looking at your pic, I'm guessing you may have to grind or cut back further. I use the 2X rule with rust - it goes back twice as far as you think and the hole is always twice as big. Plus going back further, the clean metal will help provide a good ground. Where yours looks tricky is where the panel steps back up on the left side of the pic, so you may need to make two or three patch panels to capture that compound curve.

If the tunnel is not too bad maybe wire brush it, use a rust converter and then seal it as best you can. If you feel you need a new tunnel, you may want a metal shop or professional welder to weld it in - it's essentially a structural spine of the car and I personally would want something like that to be 100% right. With full replacement floor panels for other cars, the tunnels are stamped in from one piece of metal.
 

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Um, to effectively repair rust holes… not to put too much of a point on it… you should find a good body shop. It is very likely you won’t save any money doing it yourself.
Properly (I am assuming that’s what you mean when you say ‘effectively’) repairing rust in body panels requires that the rusted area along with a surrounding portion of “good” metal be cut away, then an additional area be ground and preferably sandblasted. Note that rust can be considered a cancer. if it is not completely removed it will spread even if it is garage MIG welding projects not visible at first. After this is done, the edges of the hole are inset a bit. There is actually a tool that will put a flange in the area so a new piece of metal can be seamlessly fitted and braze in place (if you are good).
 

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Those rubber plugs were there because the C900 is a winter car. All the slop you’re dragging in on your feet eventually went down through the carpet and pooled. In their ingenuity, all you have to do is just poke that plug out and then it would drain.

If the condition of the surrounding metal is leading water IN from the bottom, it’s time to repair if not then just leave it alone.

does orio stock floor pans?
 

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The plugs on my 1991 Vert were never designed to be "popped" out, not easily anyway. They were seem sealed or some other sort of epoxy in place. I had to use a chisel to remove them. I removed mine, cleaned around the holes, POR15 the floorboards and installed new plugs. And they don't have holes in the plugs, so they are not designed to be a drain.
 

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I'm pretty sure the holes are from assembly - maybe some machine moved floorpans along that way, or they are artifacts from the forming process. The plugs were just an easy way not to have holes in the floor. I agree - I don't think they are intended to ever be removed.
 

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Yeah may be it isn’t as easy as I described - you do have that mastic coating everything - but my comment was based on observations from my childhood cavalcade of various 99s and 900s in deepest darkest Scandinavia; where this would be part of the spring checkup.

may have been a regional thing that never made it to a TSb here. I’d be interested to know what Jim thinks.
 
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