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Old 12-01-2016, 12:33 PM
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Need help with a rust repair

Hi all, not sure that this is the correct spot to post, but I am in need of some help.
My 85 300d was in to get the windshield replaced recently, but the glass shop had to cut the process short when they found a small spot of rust-through under the windshield gasket. The hole is about the size of a quarter, almost entirely concealed by the gasket. It is through to the cowl vent area but not into the cabin of the car.

I am still calling around, but so far the quote to weld in a patch and respray the panel I have gotten was $500. This is outside of my budget and I really need to get the car out of my garage soon.

Would anyone in the kc metro be willing to help out welding a new panel in? I can pay a reasonable amount and will do any grunt work needed, but my welder is a flux core unit and I am not very talented with it. I think a tig weld would be more appropriate. I can pull the dash if necessary.

The shop I talked to suggested duraglassing the hole, which would be about half the cost. I would prefer to weld in a panel, but I have had great results doing rust repair with por15 and fiberglass, but I will only do that if absolutely no other option presents itself.

'85 300D - federal spec, built in late 84. 85 300D Complete AC System Rebuild
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Old 12-01-2016, 12:57 PM
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Location: central Texas
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' Respray the panel ' ? How big an area are they wanting or needing to paint if this almost concealed by the gasket...

There is also the question of what is on the underside of that section...

Are you worried about too much heat warping the area ? Afterwards... can you reach the area with hammer and anvil if you need to ?

As an old hotroder and weldor.... it may seem odd... but with the smallest of tips and water filled towels around it... you can really do a good job if you go slow and tack it repeatedly brazing it..... make sure your fill piece is as tight as you can get it... that just takes patience...

and this is good reference material... as are the old Petersen publishing co books like the ones on custom car making ...

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Old 12-01-2016, 01:17 PM
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Here's a couple of pictures of the problem area. I'm afraid by the time I cut out the area and weld in a new one, there will be at least an inch or so that needs to be painted - but since the whole panel is only about 6" square, it shouldn't be that big of a deal to repaint the whole thing instead of trying to blend it.

Assuming that the pinchweld metal is solid enough to weld to, I don't see any risk of the heat penetrating the body - the hole is only through to the underside of the cowl (I can feel the back side of the hole from inside the cowl vent).

I've got zero experience brazing, though I could probably get the proper tools cheaper than a TIG welder. I'm hoping to find someone locally with a TIG and some skills, but if I have to I'd rather spend the 500$ on a cheap TIG than throw it away at the bodyshop. I'd still need to get them to do the respray, unless I could get some paint in a spray can matched to my paint color.

I think I can get to the back of the repair with a hammer & dolly if needed.

Does 500$ for this seem a bit crazy to anyone else? The hole is tiny and in a fairly flat spot, so I can't imagine it being that hard to shape a new piece to fit.
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Need help with a rust repair-img_0977.jpeg   Need help with a rust repair-img_0973.jpeg  
'85 300D - federal spec, built in late 84. 85 300D Complete AC System Rebuild
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Old 12-01-2016, 01:43 PM
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$500 isn't crazy at all,assuming they are going to do the job *properly* and make a little money in the process. That will mean cutting out the rust and the immediately surrounding metal, and welding in a new piece, seam sealing the weld correctly and then painting the area.

How long do you realistically want to keep the car? I don't know what the state is of the rest of the car, but unless it's pristine and you plan to keep it another decade... I would take a grinder to that rust, use one of the "rust killers" products out there on the area, then lay in fiberglass cloth over the hole. Or you could possibly use some mesh and cover the hole with JB Weld, or use JB Metal (the stick) to plug it.

Purists won't like my answer but for that small area, I would probably go the cheaper route.
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Old 12-01-2016, 01:44 PM
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I bought a custom aerosol can of matched color to my benz's code, as well as a can of clear coat, for 45 bucks total from AutomotiveTouchup (dot) com.

I'm not sure how good it will blend in areas - as I was just painting the underside of a fender lip, where it's in different light/shadows from the rest of panel.

but you can buy a can and test. it seems like a good match if your car's color has changed drastically.
Montclair, NJ
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Old 12-01-2016, 01:46 PM
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Location: central Texas
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Of course until you get in there with a powered wire brush....
and a pick hammer...
you will not know the extent of the rust which does not show from above...
but is necessary to know because you have to have solid metal to attach to...
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Old 12-01-2016, 01:46 PM
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The patch would be easy and cheap, it's the respray that's the expensive part for sure. It's just enough that the weld is going to burn into a visible area, so you really would have to repaint that whole panel. Luckily it's not on the roof part or something.

All I have access to most of the time is a flux welder, and I've done way more delicate repairs than that. You might practice a bit and try it yourself. You'll have to do a good job of protecting the surrounding area from spatter, especially the interior. Flux spatter will even melt into glass if it hits it. Lastly, Forney is the cleanest flux wire brand I've ever used so you might look for some of that to give yourself a leg up.

Otherwise I've seen many POR-15/Miracle Paint and fiberglass repairs that were permanent so for an inconspicuous area like that I wouldn't have a problem with it. It'll certainly never rust again.

Finally, you can get all the factory colors in a spray from and they look great, especially if you opt for the 2k clear in a spray can. So that would keep it all under $100 if you did everything yourself.

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Old 12-01-2016, 01:49 PM
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I would not weld. Rust hole is small and can be rust proofed and sealed. As long as no moisture can get to it, it will not rust further. Buy this DOW BETAPRIME 5504G ALL IN ONE AUTOMOTIVE URETHANE PINCHWELD PRIMER | eBay first.

Lightly wire brush the pinchweld frame to remove loose paint and rust, degrease frame with Brake Clean, brush entire pinchweld frame with the Pinchweld primer, use 5 min epoxy to fill the primed rust hole and smooth it out. Make sure the FSM glass rope-in procedure is followed or else the job will not come out right.

You do not have to buy the primer since the glass shop should have it and use it as part of the glass install, if he don't mind waiting 15 minutes to let you apply the epoxy.
85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked
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Old 12-01-2016, 02:18 PM
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2x on not welding that small hole. Seal it and cover it with something like JBWeld.

1991 350SDL. 230,000 miles (new motor @ 150,000).

Tesla Model 3. 136,000 miles. Been to 48 states!
Past: A fleet of VW TDIs.... including a V10,a Dieselgate Passat, and 2 ECOdiesels.
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Old 12-01-2016, 02:32 PM
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Rust repair is a slippery slope - I did a ton of it in my Michigan days. I agree that the repair area is almost certainly considerably bigger than the obvious flaw. Rust is like an iceberg with the majority below the surface.

I'd clean the snot out of that, making sure that the edge of the remaining metal is full, original thickness. Then make your patch. Brazing will work just fine and takes less heat and so less warpage is likely. You'll need all of the edges to be REALLY clean whether you weld or braze it. The better you fit the patch the better the outcome though if you braze it you really need the patch to slightly lap the hole as it's difficult to get a decent edge bond with brazing. Hopefully you'll be able to pull the lapped patch up from the bottom of the hole - just attach a length of welding rod to the front face of the panel to use as a handle. You'll cut that off and grind the area when the patch is in place.

There IS one other option. IF you can get the area REALLY clean both top and bottom you can bond the patch with an autobody structural adhesive. I have the Lord Fusor system and there are others. This uses a sort of caulking gun arrangement with 2 tubes, 1 adhesive and the other the catalyst. It mixes in the nozzle, which you toss after each use. A lot of modern cars are essentially glued together so this makes a completely satisfactory repair. The best part is that zero heat is applied but you do need a lap for the adhesive to have a place to be. If you can get the patch below the existing metal (like the brazing process) you can fuse the patch in place and come back the next day with filler as needed to complete the repair and make the window channel even with the existing metal (you could even use JB weld or similar for your filler). If you don't want to invest in the adhesive system you ought to be able to find a body guy who would stop by your house in the evening after work and bond your pre-made patch to your prepared body metal - might cost $25 or $50, something like that.

Wish you lived in my neck of the woods - we'd be done and sharing a Diet Coke by now.

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Old 12-01-2016, 02:37 PM
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The glass shop said it had to be a welded in patch before they would reinstall the glass. I havent seen how difficult it is to install new glass in the front of the w123 chassis yet. Anyone know if its DIYable? The car is very nice and I very well might keep it for a decade. It's got a fairly decent respray, all new interior minus the dash, and i have way more money than i could sell it for invested in it.

I think this weekend I will grab a couple square feet of sheetmetal to practice seam welding with my flux welder, anyone know what gauge is appropriate? As well as some of the flux core wire that rogviler suggested. I need some practice welding anyway. Maybe i can get good enough to do the repair myself. I have a few other trouble spots I need to fix anyway
I like the idea of buying the colormatched spray can and just doing the respray myself.

Instead of looking at this as a problem, i am going to focus on it as a learning opportunity

Thanks folks!
'85 300D - federal spec, built in late 84. 85 300D Complete AC System Rebuild
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Old 12-01-2016, 02:46 PM
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Originally Posted by Demothen View Post
The shop I talked to suggested duraglassing the hole, which would be about half the cost. I would prefer to weld in a panel, but I have had great results doing rust repair with por15 and fiberglass, but I will only do that if absolutely no other option presents itself.
If it was my car, I would wire brush, then use rotary tool to get rid of thin and loose metal. Maybe apply some rust converter. Then coat with POR. Maybe use POR-Patch which is less runny and comes in a small tube. One or two coats should do it. If there are significant holes, use some fine glass mesh to close them. Then roughen cured surface and use a 2-part epoxy like JB-Weld Steelstik or POR epoxy-putty to form the shape. May need to use tape to keep it in place while setting. Then file or sand to final shape. I wouldn't use Duraglass unless you use POR first. - I think it is just polyester resin with glass filler and metal will probably rust under it unless protected.

$500 for the repair isn't that bad and I have spent that on areas that can be seen (like sunroof edge), but for hidden repair epoxy/POR will probably do a better job that a weld where back can't be primed.
85 300D,72 350SL, 98 E320, Outback 2.5
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Old 12-01-2016, 03:11 PM
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Okay - so I'm thinking about this more, and since several people have suggested brazing, which requires less heat and won't spatter, I'm thinking that might be the better option.

Unfortunately, I'm completely out of garage space - which means buying a full size brazing rig is out of the question. (My stepfather has one, but he's 6 hours away, so that's a no-go as well).

Would something like work for what I need? I suspect I might need to buy an extra set of cylinders for it, so I could have plenty of time to practice. It looks like they recommend nickle-silver brazing rods for use with steel.
'85 300D - federal spec, built in late 84. 85 300D Complete AC System Rebuild
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Old 12-01-2016, 04:04 PM
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I would use epoxy myself and then spray with a can of matched touch up paint. I might use cloth and epoxy but likely just a viscous epoxy like Qwikmend. Epoxy doesn't rust and bonds very well. I have found the cans from PaintScratch are identical with the original color of the car.
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
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Old 12-01-2016, 04:23 PM
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I agree w/ the epoxy patch. Someday when ready to repaint the car, deal with a more proper fix. Epoxy isn't that bad, there are seams in factory cars that were sealed similar, w/ just spot welds attaching the panels. Some whole bodies are epoxy/fiberglass.

If the glass shop won't move forward, offer to take your car elsewhere and not pay them a dime. A competent shop would have offered to fix it for you. I am sure they run into such rust-thrus all the time. Seems they enjoy slapping customers down. Replacing a windshield can be done at home. See youtube.

1984 & 1985 CA 300D's
1964 & 65 Mopar's - Valiant, Dart, Newport
1996 & 2002 Chrysler minivans
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