1970 Fiat 500L Welding Question

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1970 Fiat 500L Welding Question

colburnsteven

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I was making upgrades to my 1970 Fiat 500L, and as I was installing the new 3 point seat belts, I took off the carpet in the back of the vehicle, only to find a 12-18" gap in between the floor and the door rail on the drivers side. You can physically see through and outside of the car to the ground. It's located where you would install the seatbelt harness for the front seat, but it's just behind the front door towards the bottom of the floor and sidewall in the back. I'd like to know what gauge sheet metal to use to weld this, and if that's going to be a huge problem for me? It appears to have rusted through... My concern is that while driving, I may fall through the floor if not fixed soon. lolol. Thanks for any assistance in this matter.
 

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That is not good.

Firstly you need to examine inside the sill and B post box sections to establish the integrity of what you are looking to build on.

The next step is that if the sill abd B post box sections are sound then look at the expected / wanted structural requirements. It this an area where in a crash structural strength is vital.

If vital then you I believe need a layered approach. e.g. like laying a 2 cm sticky tape over the gap. Then a 4cm sticky tape with some small holes punched in it. Both are seam welded around the edges and then on the layer above the lower layer you then spot weld through the upper layer holes.

If you try to weld a 5mm thick piece of steel to a 1mm or less piece of steel then there will not be integrity or strength. However if you think about why laminated ply materials are so strong and flexible then this will give you the guide to repairing your car. Think of applying strips and layers of similar thickness metal.

I've never had to personally do the type of repair you are looking at but the principle is sound. I do have limited experience of mig welding thin metals and it is not easy. If the sheets are of the same gauge then this this is bad enough. Trying to weld thick to thin is not easy. I'm more comfortable with 2mm+ materials where you can get a good 2mm to 3mm+ weld but even this can/should ideally be done by an experienced full time professional welder with the correct kit.

My personal view/observation/suggestions.
 
It looks like there has been a failed repair or the original metal has stress cracked. You need to check the car is not distorted. You might needto weld temporary structural tubiing inside the shell to keep it straight. Then the old metal can be cut out and new metal welded in. I think you will need to make a repair panel by cutting, hammering and welding flat sheet to the correct shape then seam welding it into place.

Only when the shell is structurally sound can you remove the support frame.
 
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