How bad does W123 floorpan rust look to you?
 

Colleagues,

Bought my friend's 82 300 Turbo. The good news is, he replaced the engine 70,000 miles ago with an OEM 617 and the compressions are like brand new. The bad news is, I pulled out the interior this week and saw this on the driver's side floorpan (pictures attached). I'm new to the make and model, so I would appreciate your help.

Couple of comments/questions.

1. The pan is rusted right beneath the left rear driver's seat bolt entry on both sides, but the stiffness and integrity of that little bracket is remarkable. I couldn't get it to flex even 1mm, and I think all that it's attached to is the floorpan and a bit of the side of the rocker panel.

2. I think the picture shows it all. All the rust, I mean. The black trim around the rust spot is where I pulled back the asphalt coating to find good metal. It stops in the rear about 5" in front of the rear suspension bolt, and in the front where you see it.

3. There is rust up and underneath the side of the rocker panel (see where the side is eating it's way up to the seat-belt bolt) but I can't figure out how to get in there to check things out. What's the secret?

This car is great, and runs like a top. Transmission was overhauled 30,000 miles ago. So I figure if I can fix this, it's good to go for another 250,000 miles at least. Which will probably outlive me, since I only drive about 5,000 miles per year.

The advice I get ranges from

A. You're doomed. It's pointless to continue (Merc dealer).

B. Get in there pronto and cut and weld a new floorpan.

C. Wire-wheel it to bare metal, top and bottom, and JB-Weld some 90-degree brackets or sheet metal. Then rust proof it. Then you're good to go for another 10 years.

D. What's the problem? Oh, that. Throw a little carpet on it.

I'm somewhere between B and C, above, but I'd like your opinions.

Thanks in advance.

Matt

B and 1/2 would be the option for the car and the conditions you set.

Cut the rust out, form a new panel and lap weld it to the existing good metal. Coat it with some POR15 top and bottom and drive the beastie.

If you were gonna restore it I'd say, cut out the floor pans and re-weld but, since you are just going to drive it then make it work.

Either pop on over to, uggghhhh, Harbor Freight, to pick up one of their $49 sheet metal brakes or go to a metal shop to have them bend you a replacement section.

Minimum 16 gauge and I'd recommend 14 gauge. Wire feed weld the booger in, rust proof it (top AND bottom), slap some carpet on it and go.

Oh yeah, either replace the wind screen gasket or the door window stripping, whichever is leaking the water.

note to self, fix the water issue

My plan
 

That's what I'd do. But with a really good engine and transmission, I'd also watch ebay and try to pick up a rust free original with a bad engine or transmission. Swap all the good stuff into the best body. Rust is apparently a real issue to stop in these 123s. Being in Texas, I have none.

Water leak diagnosis
 

Good advice on the water leak diagnosis. I shall attempt that, anon.

It hasn't rained a drop since I bought the car in LA, and now it's in Boise, Idaho. Also dry as a dog's bone up here, as well. The car hasn't been wet a single time since I bought it a month ago.

What's your hypothesis, given the location of the corrosion? All the seals and rubber in this car are old, unfortunately. It's been driven in such nice weather for so long (a contrast to it's early years in salt-laden Ohio, I might add) that I don't think my friend ever saw the urgency for seal repair.

I pulled off the driver's door panel and there is definitely whitish, corrosion-ish 'crud' globules accumulating at the bottom of the glass, where the glass tucks into a metal strip that is supported by the regulator. However, the bottom of the inside of the door looks pretty clean.

Are there any drains that could be stuck somewhere that could cause this? The passenger side floorpan looks fine, even though the passenger window seals look like they've been through a Cuisinart. They don't look like they could repel anything, yet there is no corrosion I can see on the passenger floor. Could it be a drainage issue? I'd like to see the inside of the rocker panel but I can't figure out how to do it.

Matt

123's are prone to windshield seal leaks and rusting out of the hood hinge pockets. Both of these lead to water leaks into the interior. The water drains downhill to the floor pans - sometimes under the carpet. The carpet may feel dry but the water starts the floor pan rust. It's a cancer that once started is hard to stop and repair.

I'm having the same issue on my W114, something from the windshield area is coming into the cabin and rusting my pans from the inside-out :mad:

I'll be watching this topic, but the first thing to do it stop the water from coming into the cabin, then cut out the old stuff, weld in some new pans or parts-of-pans and drive.

Best of luck.

Much better than the floor pan on the drivers side on the car im parting out due to a fire caused by a welding accident. You dont need to cut out 3/4 of the floor pan like i did. All you have to do is make some patch pieces and your good to go. I also see rust where underneath the front seat support.

Wish my floorpan was like that.

There are a series of videos on youtube which address floor repair for Mercedes. It is slightly long-winded but provides some good ideas for securing fabricated floor sections to the body. He drills temp screw holes for the door frame side then welds the other edges.
Once secure he removes screws and puts in rivets. (Welding on door frame side might overheat frame and affect door closing)

Estimates for repair
 

Well, I drove around Boise to about 10 body shops to get them to look at this. Only 3 even were interested. The other 7 said 'we don't do that kind of work any more'. Hmmm.

2 of the 3 estimates were to clean it up, cut out a portion of the inside wall on the rocker panel, and weld in a new sheet of contoured 16 gauge. Seems reasonable. 10 hours estimated labor at $50/hour, plus about $50 for sheet metal. Both estimates were $600-ish and they said they needed the car for a day.

The other shop insisted that welding was unnecessary, and that they would 'glue' (their words, not mine) metal in to cover the hole. And that would be as good, or better, than welding. I pressed this a bit, but the guy was adamant that was the way to go. $200. But I think I could probably do that myself.

I think I'm going to go with the $600 weld job. The more I drive this car, the more I like it.

You can buy yourself a mig welder for $500. Add in the $50 for the metal and in the end you'll be $50 ahead. As a bonus, you'll have a mig welder left over.

Yeah, but I'll probably be dead
 

I don't trust myself with welding just yet. Gotta work my way up to that from snipping and riveting. :-)

idaho,

haha, this looked just like my car! read my blog in my sig. start from the beginning :D

You've got to start sometime. My first welding was on the SS exhaust. I've never had a problem with it yet. My second was the trunk repair - not perfect looking like an experienced TIG welder might do, but fully functional and covered with seam sealer. If you are not doing cosmetic work then it is okay to make a few mistakes along the way. You can always plug up your burn holes with more material. Cover it with seam sealer when you're done and only you will know what it looked like, but everyone will see that it works.

The exhaust system was your FIRST welding project? Wow! I'm impressed, Paul. You did a great job on that.

Where'd you get your welder? What did you pay for it? I've done gas welding before, but not arc or tig/mig welding.