Question for welders/auto body experts?

[speeder]

I have an old Mercedes w123 w lousy paint and some strange rust along the lower rear window line. Not a spot of rust anywhere else on the car, I've looked everywhere.

This car is not worth restoring or repainting, w123 sedans w some miles on them are worth a few thousand dollars in really clean shape. This one has terrible paint, (clear coat failure from sun), but it runs like a scalded monkey getting chased by a lion. It belonged to an 85 y.o. German friend and was always maintained by my other friend's MB shop, the best in town.

Bernie had to stop depriving and I bought the car. I'm fixing all the random issues on it and selling it to a young lady who just needs a car. I don't really need to fix the rust but the "fixit guy" in me wants to do something about it and just spot paint it. Cars like this that don't really matter are great to learn on.

So what is a proper repair here? Obviously, the rear window comes out but then what? Weld it up and grind it down? Braise(?) it w bronze? I know zip about this stuff but want to learn.

I ground the rust down a little, it's pretty bad.

[john walker's workshop]

I'd Rust-Mort the remaining rust, trowel in some Marinetex (JB weld) sand smooth, bomb can and call it a day.

[drkshdw]

Proper would be to find a dry replacement panel to weld in to eliminate all the fried metal that you can't see underneath. Next best would be to just weld the holes and grind smooth. If this really is going to be a beater that will never be restored then Bondo over it and be done with it. Or if you want metal in there, go old school and use lead. It's super easy to work with.

[LEAKYSEALS951]

maybe just me - but it looks like there is potentially older filler already to the right of the larger defect.

[1990C4S]

Window out, clean, braze, lead, or mig. Your choice.

On a cheap car I would acid etch it, prime it, and add bondo.

[speeder]

Originally Posted by john walker's workshop

I'd Rust-Mort the remaining rust, trowel in some Marinetex (JB weld) sand smooth, bomb can and call it a day.

Not familiar w those products but sounds like a good plan.

Originally Posted by drkshdw

Proper would be to find a dry replacement panel to weld in to eliminate all the fried metal that you can't see underneath. Next best would be to just weld the holes and grind smooth. If this really is going to be a beater that will never be restored then Bondo over it and be done with it. Or if you want metal in there, go old school and use lead. It's super easy to work with.

You are absolutely correct about the proper repair but not going to happen on this car @ this time. Probably bondo and rattle can it.

Originally Posted by LEAKYSEALS951

maybe just me - but it looks like there is potentially older filler already to the right of the larger defect.

Good eye. Definitely bondo present from a previous accident.

Originally Posted by 1990C4S

Window out, clean, braze, lead, or mig. Your choice.

On a cheap car I would acid etch it, prime it, and add bondo.

As above, this is the correct answer for a proper repair but not spending $$ on it. I have a friend in the neighborhood who is an amazing welder, (not a car guy but an artist), had thought about having him weld some metal in it but leaning towards bondo now. Believe me, if it was a keeper that was worth anything, I'd be doing it right.

Thanks again for the quick replies.

[speeder]

Still can't for the life of me can't figure out how it rusted in that location in SoCal. We have what's called "beach rust" here if a car is parked very near the ocean, (close enough to actually get ocean spray in the air), but normally it would be present in several locations.

[Charles Freeborn]

What John says. If you start grinding and welding it will spread to a MUCH larger repair project. The cause of the rust was / is a leaking window seal. If you like the person you're selling to, you could pull the glass and re-seal or replace the window seal to stop further decay. Would make the repair easier too. If you're uncomfortable pulling the glass take it to a glass shop and have them do the R&R.

[speeder]

Originally Posted by Charles Freeborn

What John says. If you start grinding and welding it will spread to a MUCH larger repair project. The cause of the rust was / is a leaking window seal. If you like the person you're selling to, you could pull the glass and re-seal or replace the window seal to stop further decay. Would make the repair easier too. If you're uncomfortable pulling the glass take it to a glass shop and have them do the R&R.

I like her, she's hotter than molten lava. But it's a cheap car to get her around town and no matter what I do, I doubt it will rust more in this climate. I'm going to hit it w red oxide primer, bondo and rattle can it.

I'm aware that leaking window rubber seals can cause rust but it's so much more significant than I've seen in the past in this geographical location.

[john walker's workshop]

We need pics, and not of the car.

[speeder]

Originally Posted by john walker's workshop

We need pics, and not of the car.

I'm surprise that you'd ask.

I'll see what I can do but I always think of the consequences if she found out she was being graded on a car forum.

[1990C4S]

Originally Posted by john walker's workshop

We need pics, and not of the car.

The buyer. NOT the seller.

For the most basic repair, POR15 is pretty good....when done properly.

And she's not be graded. We are simply confirming the veracity of your story.

[VincentVega]

Maybe it sat a lot and was parked at an angle that kept water small corner between the glass and the trim. Seal cracks and shrinks with age and traps more moisture.

[wdfifteen]

Originally Posted by john walker's workshop

I'd Rust-Mort the remaining rust, trowel in some Marinetex (JB weld) sand smooth, bomb can and call it a day.

+1
Dent it in 1/8 inch or so so the epoxy (JB Weld) still has some thickness after you sand it. It's this or turn it into a huge project.

[T77911S]

osphoric acid on the rust first unless something better has come out.

if you can get to the back side, put JB wled on some masking tape and then tape it up there. the tape can help hold it in place. spread excess around on top.
sand it then bondo.

[304065]

Denis, if the rest of the car really is clean, then fix this right.

I don't have to tell you what that means. Remove the window, start grinding back.

I see existing bondo which means it's going to look a LOT worse underneath.

Get it back to bare metal, get a piece out of another W123 that didnt' make it, weld it in, metal finish.

Do it right. Karma man, Karma. So it costs more money so what?