The original floor pans looked solid but on proceeding to strip them on both sides this revealed a number of small holes in various places. I spent many hours on my back scrapping off the old paint, which just peeled off. I used a blunt chiesel and 3m stripping disc's mounted on a drill to quickly proceed to bare metal.
I decided to replace the complete interior floor pans with new replacement panels. The seat support boxes again looked solid but on cutting these out revealed that these were rusting from inside out and would have eventually collapsed. Mercedes-Benz never painted primer or sprayed anything else on the insides of the frame and box sections of the 190SL, which means that the insides of all box sections are prone to rust. The entire frame and floors should be inspected properly. The best method is to use a pick hammer and tap each part being inspected as described in The International 190SL Group's book Mercedes-Benz 1955-1963 Restoration and Ownership.
The floor pans and seat supports were cut out by drilling out the original spot welds with a spot weld cutter. The resulting spot welds were ground down. With all mating surfaces smooth and further welding to damaged chassis lips the chassis was sandblasted and then acid washed. All inner box cross sections were primed with PPG DP40 epoxy primer and sprayed with Wurth cavity wax.
The floor panels come in four sections, left/right and front/rear. Although these came from Mercedes Benz the quality was much to be desired. The rear left panel required very little cutting and adjustment to make a perfect fit, but the right rear was a few cm's too long all around and was not pressed in the centre of the panel. This required many hours of measurement, cutting, grinding and trial fitment before the panel was ready for welding. I have heard of left rear quarter wings being out of alignment too. All I can think of is that these parts are reporduction and not pressed from the original tooling.
This photo shows a trial fitment of the floor pans, which were aligned and marked up before cutting. Notice the original blue DB334 colour of the car evidenced after removing the sills in the lower left of the photo. The car has had its colour changed to black DB040.
The floor pans on a 190SL are originally lifted up onto the chassis from underneath and spot welded to the lip of the chassis members. Spot welder arms would not reach as the outer panels were fittedby the factory after spot welding the floor pans. I wanted to keep the look of the floor pans as original as possible. The only way to achieve this was to plug weld. A punch/joggler was used to punch holes every inch or so. The resulting plug was welded from the centre in short busts to the outer edge of the hole. This inverted welding position took sometime getting used and to set the mig welder and wire speed correct as I was welding in the inverted position. The floor pans and the part I was plug welding onto were 2mm thick so I had no problem with burning through. To stop the molten weld bead dropping out onto you, you need to strike the centre of the plug with the wire hot and fast. The resulting weld bead was then ground flat. As an additional security I stich welded the panels together on the inside of the car. The factory stich welded in serveral places inside the car too.
