the driver side is almot perfect but the front passanger has a big hole. how can i fix it without welding
Well first fix the cause of the rust. Which sounds like a leaky heater core or cowl. If its an AC car it will only have one cowl opening which is on the passenger side. If the hole isnt too big you can try rustbullet+fiberglass mat. Go to the tech article section for the "How To" on that.
I agree about first finding the source of the rust. Fix that problem first to prevent future rust from coming back. To fix the rust hole and expect the rust to not come back is next to impossible without some degree of welding involved. The only way to correctly fix the problem for good to weld in clean, new metal. If you just can't go that route you can pop rivit new metal in place. All of the rust surrounding the rot hole would need to be cut out and the exposed metal treated with a rust preventer like Rust Bullet or something similar. This should be done both inside the car and underneath. Next get yourself a piece of sheet metal cut to fit over the rust hole with some overlap. Use a hammer to contour the replacement metal so it fits as close to the existing floor as possible and pop rivit in place. It would be a good idea to put some seam sealer all around the edges of the new patch both inside and underneath the car to act as a water barrier. Spray some self etching primer on the edges first so the seam sealer doesn't crack. Finish the job up by undercoating the patch underneath the car. While this is not a permenent replacement patch it should last for a good long while.
If you do go the patch route at least get it bead rolled. My local body shop only charged me 3 bucks to get a panel rolled. Its well worth the money for the added strength.
To add to Jean Doll's post, once you get the patch pop rivited in, you can fiberglass over the entire section of the floor. That will add strength as well as waterproof it. Like Dan said, it will still be patched, not fixed. Only way to truly fix is cut out the rust and weld rust free metal in it's place. You might be able to find a donor piece from someone who has a parts car. Then you could always take the car to a welder and let them weld it in for you.
i know exactly what caused it.. 3 years without a windshield.. its kind of amazing thats the only serious rust spot.
I bet that rust was there even before the windshield went missing. If that was the reason then the other floor board would be rusty also. Ask the AC guys, most of their cars only have the passenger side rusted out. Mine was the same way, and its been an AZ/CA car all its life. I would pour water in the cowl just to make sure.
