Appreciate advice on rust repair [Archive] - SaabCentral Forums

: Appreciate advice on rust repair


silversaab96
10-01-07, 08:04 PM
I just discovered some rust hiding under some sheet metal in the upper firewall (see pic).

The rust on the RHS (of the car) is only surface rust, but on the LHS as you can see, it is all the way thru. As it is all flat, I'd imagine cutting out the rust and replacing would be a fairly straightforward job, but I'd appreciate any advice on the best way to do it so that I can make the repair invisible once resprayed.

I was wondering if, once the rust was cut out, i could cut some sheet metal to the same same size and shape of the hole, bracing it from behind so that it is flush, and welding the new sheet in with a number of small spot welds, then maybe even following on with a seam all around that can be then ground down.

I know sheet metal can distort and "shrink" when welding, so what is the likely success rate of trying to do what I'm proposing?

Or is there a better way?

Cheers.

Si
13-01-07, 07:36 AM
Have a look at the thread ' you guys and your rust repairs' in the 99 forum, loads of good info in there.

silversaab96
13-01-07, 07:39 PM
Thank you Si(re). ;)

dougsaab
14-01-07, 05:24 PM
That is my thread over in the 99 forum. It might help if you had more pictures of what you are dealing with. What is underneath where all the rust is? From what I can see, you need to start removing everything that's in the way, then evaluate further. Some rust looks OK until you start grinding and probing, then the holes open up.

I thought cars in OZ didn't rust?

silversaab96
14-01-07, 05:33 PM
Thanks Doug. A damn fine read too. I'll post another pic or two, perhaps closer up.

As for the rust, it's an ex-UK car, and has only been here 2 years. I'm only just finding the time to get it all sorted for a roadworthy now. A fair bit of rust in the floor, but that was done over a year ago, and only minor things to do now, but I found a piece of sheet metal sitting over this hole and pulled and prodded til it came out, and found this big hole, and just want to fix it properly. I've poked around with a screwdriver and it appears to be no worse than what you can already see.

dougsaab
14-01-07, 10:26 PM
I have no knowledge of how 96's are put together, but I know rust repair. If I have to study an area for months before actually making a cut, that's what I'll do. One of my concerns is what is below all of that rusted metal? underneath the dashboard? wiring or flammables in the way? Do you even have access? is it structural?

I also see that the rusted piece is spot welded to the vertical panel, and the rust goes underneath the seam. You either cut all of it out, or media blast it. That's the only way to get rid of all the cancer. Finding and drilling spots welds is not that bad to do, but if you can't get to the backside of that rusted panel, that may be a problem. Does that panel stop where it is spot welded? If so, then it might not be difficult to fit a new piece. The wiring going thru the hole would most likely have to be removed...make a template of your patch out of thin cardboard(before you start removing rusted metal so you make it as accurate as possible, trace it onto a similar gauge of sheet metal, cut it out, fit it, weld it

cardboard template

http://saabpics.com:3000/gallery2/d/105254-3/P9080001.JPG

some welding tips are here

http://members.lycos.nl/mhilvers/welding.htm

Warpage is always an issue, but spot welding repairs keeps the heat down. Spot welded(not to be confused with tack welded) panels are actually stronger than continuous welds, that's why auto manufacturers build cars that way.

You can make the patch bigger than the hole(alot easier to do then trying to make an exact fit patch), either place the patch above or below, drill holes, make spot welds, grind welds flush, use seam sealer on both sides of the patch to keep out the elements....or you can use body filler to make the patch invisible. Of course that will take longer to do.

silversaab96
15-01-07, 02:54 AM
Thanks again for all of that Doug. To answer your question about the panel, what is behind the rusty hole is air, once you remove a little bit of lining on the inside of the firewall - it is readily accessed as it is up under the dash, but the 96 dash is not deep (vertically), so this area is actually slightly below the level of the bottom of the dash, rather than directly behind the dash, so it is not going to require removal of the dash. More to the point, I can cut it out from inside the car more easily than I can from inside.

I'd rather have the repair invisible, so I guess that means the patch goes on the inside and I fill to make it flush.

dougsaab
15-01-07, 11:25 AM
Looking at the rusted area again, I think it would be alot less work if you only patched the area where there is the hole. Can you buy POR15 products in OZ?(edit: yes you can..link below) It would be easier to just coat the areas with surface rust to seal it forever. Grind the rust, treat with Metal Ready, 2-3 coats of POR15 rust paint, sand, prime, paint with whatever product you are topcoating with.

http://www.ppc.au.com/

There is also a product called Rust Bullet, but I have never tried it

http://www.rustbullet.com/

If you have access to sandblasting equipment, that of course would be the BEST repair to make. The rust creeping under the seam would be the only spot that would concern me, as there is no access unless you separate the panels.

silversaab96
15-01-07, 07:29 PM
Thanks Doug! You're a champ - exactly the sort of help I was after. I had only intended doing the hole and treating the surface rust as you suggest.

Incidentally the rust under the seam should be accessible, as the two panels are separated. There were spot welds joining them which have been drilled out. The sheet metal I removed had been slid up between them and went most of the way up toward the windscreen bottom, and extended down over the rust hole.

There is some rust around the hole where the wiring comes thru on the RHS, but it's smallish and can be done with fibreglass. I did a bit of similar work to a rust hole in a Volvo 142 door some years ago so have enough skill to tackle that job.

Many thanks again, and I'll post progress pics when I start on it in a week or two.