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Len Gates in the UK provided this important caution: on any repairs that require welding, cover all the glass on the car and on any other cars in the workshop where you're working; weld spatter travels far and will bury itself into the surface of any glass it hits. You can get it off with an acrylic scraper but the glass will be permanently pitted. This also applies to grinding sparks.
I just finished doing some repair work to the floors on my Sundance... Now I
don't know the extent of the rust on your car but in order to do a solid
repair you're going to find that you will have to remove metal about an
inch or two beyond where it is rusty. Normally where you see the rust and
holes, the metal is bad underneath the paint.
It's best, if you have the room, to completely remove the seats, carpet and
the lower interior plastic (kick panels and sill moldings) If you can,
unbolt the seatbelts as well, but most times those bolts just don't wan't
move so you may have to cut the carpet around them.
With a good view of the floor you can inspect the frame inside the car. It's very important that the framing is in good shape. If the rust is right into the framing in these areas, it's quite possible the whole car's body is distorted. You should be able to tell by the way the doors close and line up.
Sounds like loads of work but believe me it's better to do all that, then patch it up from the outside only to find the frame inside is shot down the road. When I'm doing this kind of work this stage is sometimes causes me to scrap the car.
The way I look at it, if the framing is still good inside and out, any car
is repairable :) The framing also gives you something to weld to.
When I patched my floors, my driver's side floorpan right up underneath the pedals was bad. I got my saws-all out and began to cut all the bad stuff out. I found I had to go about an inch beyound the rust all around. If your car is bad around this area and the otherside be sure to inspect where the K-frame joins to the frame rails underneath and look at the rear of the frame rails to see they are still solidly attached. When you start cutting out the rust make sure you are careful not to cut something on the other side too!! I allmost went through a brake line on mine.
I used metal from the roof of an old car that I had saved before I scrapped it. This metal is normally of heavier guage and works well for this kind of job. I used a little 110volt mig welder to do my floors, its the best tool you could invest in believe me, but I'm sure you could torch weld the floors in too.
As for heat distortion, when you weld in the patch weld them in spots. I spotted every inch on mine and never warped anything. The cars are put together with spot welding anyway. You just have to make sure you seal both sides of the repair when you are done. Doing it this way, makes forming the floorpan easier too. You can use the heat from your previous weld to pound and shape the next spot. Be sure to cut your patches bigger then the spot you want to fix as well. Don't be afraid to overlap in areas either.
If you do have to replace the floorpan metal running over the two main frame rails.. be sure to weld the patch to the flange on the rails too. The floor pan does help stiffen the chassis. Thats the joy about unibody cars *NOT* hehe... Not like the old cars that had separate frames and bodies.
I don't like saying this to anybody, but if the framing is in really bad shape, rob what you can in parts and get another car. I hate telling people that, but I am speaking from experience :)
Let us know if you have a different perspective or method - write to us!
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