Floor board replacement: Accepted/correct method?

[seattle_Jerry]

I'm getting ready to replace my driver's side floor boards and already have the metal from K&K. Whats the method everyone uses for the project so I will know what to look for in/ require of a metal guy?

For example: 1. butt welding the panel  2. Using a flange tool to create a recess for the panel to sit on then welding. 3. Is there a way to undo the original and then plop the new one in?

[George Des]

Jerry,

These floor panels are held in by multiple spot welds around the perimeter of the panel. Your metal guy will have to remove these spot welds with a rotatay spot weld remover. It looks like a small hole saw--just need to be careful to remove the spot weld from the top panel and not go through the flange below. Once all the spots are removed the old panel should lift off leaving a flange with raised bumps where the spots were. These will need to be ground down so the new floor panel can be laid on top of the flange and spot welded or plug welded in place.

[Benz Dr.]

MB never made floor pans as a replacement part.
 
Once you get the old pan removed you will see the rail that runs under the front floor. Place the floor in the car and adjust until it fits. From underneath the car, mark the relative position of where this rail sits on the bottom of the floor pan.

Draw out and mark where the top of the rail would sit against the bottom of the floor pan so that you have two sets of parellel lines the same dimension as the top flanges of this rail under the floor. Drill 10mm holes in the floor pan every 20mm apart or where the original spot welds would have been. Grind any chips off around the drilled holes so that the pan will fit nicely against the rail and plug weld trough the drilled holes. Once you are done it will look just like a factory build.

You can butt weld the front firewall if it needs to be replaced which it likely will. I would only cut off what's rusty and you can use the same method to plug weld it to the frame rail as used for the floor. It takes a lot of cutting and fitting to make a good fit for butt welding and you can easily burn through with a Mig welder. Really good welders use small gas torches to melt the steel back together but I wouldn't recomend trying this unless you know how to do it.

Seal the outer seams from the under side of the car and seal the inside as well. We use a type of gravel gard or under coating on the floors and a sound deadening on the inside of the car.
Although I used to do this type of work I now farm it out to local body shops. It's hard gritty work and I just can't do it anymore...

[seattle_Jerry]

Thanks I plan to hire it out myself as it seems like one of those things that I could make the car worth less by doing. I just needed to know what to ask for/require for a good job.

[dseretakis]

I would add that weld thru primer should be used on the mating surfaces of the floor pan and frame rail.