W202 Floor pan welding - How much interior do I have to remove?

[EdGasket]

I need a couple of rust patches in the floor pan welded and possibly some inner sill, towards the rear half plus front of sill where the underwing shield covers it. I assume the floor carpet has to come up and it looks like I need to remove the following:

1) Sill covers
2) Scuff plates
3) Both front seats
4) Centre console
5) Possibly the lower part of the side frame panels

That should release the rear part of the interior flooring. Not sure about the front part as it goes up behind the pedals and dashboard.

Relative thought he could weld it with the carpet in place and just propping up but looks risky to me. Can anyone who has done floor pan welding give advice on this? Are there any short cuts or does the whole carpet have to come out? Also what is involved in getting the front half of the flooring out?

 

[bladecrazy]

I would remove whats needed as the heat will light up the carpets very easily , anything plastic will be the same, i know my mig gets very hot.

 

[daveenty]

As above, if it's flammable, take it out. All it takes is one spark and the lot will be up in flames.

I've recently put new floors in one of mine (not a Mercedes) and stripped everything back, even including removing any stray underseal which also lights up pretty easily. A welding blanket comes in handy as a bit of a preventative measure but nothing beats a competent mate with a fire extinguisher on hand.

 

[Snake Charmer]

You want to see both sides clearly so anything within 2ft or more of the original hole to start with.
Little holes marked by the Mot tester will keep growing untill you find solid metal, expect
The outer underseal will burn and self ignite, the sound deadening inside too. Look for any wiring, manufacturers run cables in odd places. Protect the glass and interior trim if you like the car.

I was asked to do a repair on the front left chassis outrigger of a W208, something had poked a small hole in the rubberised underseal revealing a corrosion hole. The whole outrigger was rotten and had been full of water for years due to a failed plastic bung further up above. That little hole ended up with a complete outrigger, part of the chassis, inner sill and 18" of floorpan.

 

[brandwooddixon]

As above.
Lift the carpets. You might not need to remove the centre console, but it sounds like removing seats and carpets is needed for better access.
MB like to place wire runs in plastic conduits under the carpets along the sills and footwells.
Too many things that can be damaged or catch fire.
Sure your relative can try it, but do you want to risk that "Oh sh*t" moment as something under the carpet starts smouldering or catches fire?

 

[EdGasket]

Thanks. I'm in the process of getting the carpet out which I think will need the centre console removed or at least loosened at the back. Also both seats have to come out and then I think there is some air ducting screwed to the floor. I hope the whole lot isn't rotten!

 

[daveenty]

I hope the whole lot isn't rotten!

This was one section of mine after cutting out what was thought to be a 2 or so inch square bit of rusted metal: -



The bit towards the back (left of hole) also had to be cut out and replaced . It took a little longer than anticipated.

 

[00slk]

Oh, this looks so familiar......from a retired car restorer.....

 

[EdGasket]

Mine doesn't look too bad. How far away do I need to get that big electrical cable? It goes through a hole at the back of the chassis so I can pull it up some but it will still be within inches of the weld area.

 

[brandwooddixon]

I reckon you'll need to cut almost back to or under the cable to find good metal.
By some plumber's heatproof mats, wrap under the cable to lift it up and fix it as far as it will go and you'll probably be okay as long as its not touching the area that you're welding.
If the area where it passes through the floor is very close and not a good location to wrap the heatproof matting around it, you can try packing the area with soggy bread, a bit messy but works for short term protection.