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Body workers/sheet metal workers HELP

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volaredon

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This can apply to any brand of truck.
why is it that whenever Rusty sheet metal gets cut out and a patch put in, it looks fantastic once finished and painted for a while but after a year or two rust comes thru the paint and you can tell EXACTLY where it was cut out and where the seam between parent metal and replacement is?
I notice this all the time. Pull up next to someone who has had patch panels put in over the wheel wells and it sticks out like a sore thumb.

i have a 96 Dakota and 2 summers ago I replaced the passenger side rocker panel. Now I can see thru the paint exactly where I MIG welded the new to the original. My son has a 99 Ràm 2500, same story on his truck bed especially over both wheel wells and I think that his were panel bonded in place. That truck looked awesome when he got it along with piles of receipts for panel bond , patch panels paint and such. So that would rule out heat affected zone induced by welding in the new metal. He will be looking for a new bed for that truck. I have an 85 Dodge pick up that I will be doing some body work on, this summer. It needs some repairs to the wheel wells on the bed and I will have to replace 1 rocker panel on account of being smashed in, not due to rust.
since rust free truck beds don't grow on trees I will be replacing what metal needs to be on the existing one. (This one isn't as bad as some trucks around here that at almost 30 years newer, but I do not want to go thru the work knowing that in 2 years it will look worse than it does now)

i also know that most patch panels sold on the aftermarket, are imported. Is there something like dissimilar metal composition between original American steel and these patch panels?
being as how my son's patch panels were bonded and not welded I am beginning to think that I can rule out the welding as being a cause.
I also have a plymouth volare that I have done some body work on (that one is still in progress) and I have some solid patch panels cut from other dodge aspens and plymouth volare's in the junkyard years ago. Will using patch panels cut from actual cars the same age, using the same grade sheet metal as was used on the car to begin with// vs aftermarket parts, have any effect on preventing this problem?how can it be prevented?
 
"following" I have a few questions. What type of filler was used over the weld? Plastics retain moisture. Where the weld areas ground to metal before welding? Using a weldable primer may be a better choice just don't know. We use to primer sealer before putting down any type of filler that way moisture cold only travel one way even if it got trapped under the finish coat. Hope someone has a definite answer for you.
 
I know what your saying as I have seen the same thing on repaired box sides and rockers. Is the rust reappearing is these areas or the panel seams just visible? If it's it rust, the original metal may need a rust converter. I agree with @7mopar about putting filler over bare metal, always use a epoxy primer to seal the metal before the filler.
 
Most of the ones I have seen do this, have been primarily right at the seams. On the rocker panel on my 96 Dakota, I flanged the existing metal with a crimper/ so the new piece would sit flat, and since this is a work truck, I just painted the rocker with NAPA's version of white POR-15. (rest of truck is white) I didn't use any filler. It's down low and the lack of a finished seam is less noticeable than holes were. Until the rust bled thru. and I cut back to good parent metal, that had no rust when I cut into it. I still have the remaining piece of that new rocker panel here. I thought that I could cut out a section to fix the other side, the parts of the stamping that make these side-specific, I won't need on the other side.
I cant speak for the ones I see, such as when I pull up next to them at a light..... I wasn't involved in those repairs.

On my 85 I was gonna buy patch panels, (can cut most of new patch away, mine are not that bad) and still might; but I found a screaming deal on a pair of factory bedside cutoffs,,, whole complete bedsides, I'm either gonna drill all the spot welds and replace the whole panels with these, or not gonna use them at all.....the problems with my originals, are more dents and a caved in pass side (but not creased, I have 90% of it popped out already) due to an 80-some year old past owner that could barely see..... I have some pulling to do back by the taillight on the other side, if I don't just replace the whole bedside.

I'm not gonna cut up these nice new-to-me, bed sides I got. (I don't have them in my possession yet, were an Ebay buy, got a road trip coming up to go pick them up)
The only one I have been involved in that never did what I am talking about, was the cab corner on my old '79 that I did about 30 years ago. that one came out the best of any I have done, and never rusted like this. I dunno if metal quality on patch panels was better back then (I'm betting it was, even if that isn't the reason for the issue) but I wonder if results may be better/longer lasting, if patches of original metal from another of the same kind of vehicle, might give better results. I dont care if it is body or mechanical, I HATE RE-DO's. Having to do the same job 10 times over on 10 different vehicles doesnt bother me.... though it does get old. but the 1st one of those 10 jobs that I have to repeat on the same truck? That does piss me off. and especially body work, it is more intensive and typically the truck is down longer than, say a defective water pump that needs replaced a 2nd time, if you get what I mean.

Being as how I see this mostly right at seams where new joins old, I am leaning toward the cause being something to do with dissimilar metals in contact with each other.
Yeah, you're joining sheet metal to sheet metal.... but "metal" is a much broader category than a specific alloy or mix of additives in a given grade. (not saying I would use this) but aluminum is even considered "metal" as is stainless (many grades within itself) titanium, and iron based. and having worked in a steel mill, and seeing the process and testing while a given heat is in the furnace, the adjustments to get what the customer ordered, and sometimes yeah/ even rejection of a whole batch, there is a difference. sometimes they went ahead and made billets from the rejected batch, (some of those got sold to someone else with different specs, some got cut up and melted back down, we even poured out a few batches into a "slag pit" and started over.

is there a "special" mig wire that will prevent this? Looking at my son's truck that point may be moot. though he bought that truck "already done", and I wasn't around to see exactly how the repairs were carried out.... unless I start grinding on his truck to see how the PO did that job I can only guess based on reciepts provided by that PO for suppllies. IDK if they were at least partly welded and then panel bond used as filler or if they were strictly hung by panel bond. I know the pass side back door has either bondo or panel bond around bottom of the door at least 1/4" thick..... that truck looked real good when he bought it but over the year and 1/2 or so he has had it it has fallen apart before our eyes.
Ive seen paint jobs that look as good 15 years after they were done, as they did a week after they were done.......which is what I am after. and I've seen them fall apart within a year after paint and body work.
I know myself, what limited amount of body work I have done, I do all I can to keep bondo usage to an absolute minimum.

but, they wont be making 76-80 Dodge Aspens or Plymouth Volares again, or 80s Dodge trucks again, at least "as they were" when they were being built so any work I put into these, I need to last as long as possible. paint is crazy priced these days, another reason I need this to be right the 1st time, and not have to be redone. It will definitely help being that neither of these vehicles I am talking about, will come out of the garage again in salt season, once done.
 
Rusted out 90's truck yikes that doesn't happen in s.cali..good luck with this, I would have to guess that the metal type is not an exact match and may be causing a reaction of some type. I know that in some areas you really need to test the mineral in the ground if you lay down metal pipes. As trace metals in the ground can damage the pipes so to speak and cause leaks and breaks.
 
My son is looking for basically a whole rust free body to switch out with his present one. Whether that's a whole truck that isn't running or whether that means a door, a fender, a bed at a time.
He has other (older) vehicles that will need some body work and so do I. He has a 72 plymouth fury wagon, an 80 D150 (that one don't need much, it's from the South)
And I have a 78 sport fury, (that one don't need a whole lot either) an 80 volare (that is apart and in a homemade rotisserie, and has been for too long) and my 85 D150 that all need varying amounts of sheet metal replacement.
In the last week I bought 2 complete cut off bedsides 4 states away from home (Illinois) that I have to go get here soon.
It will be probably about the same amount of work to drill out all the spot welds on both my bed, and the replacements /and tack weld the rust free bedsides back on, as it is to cut out the rust and weld in patch panels. On my volare I have some NOS replacement sheet metal, and some good used cutoffs from back in the day.
On the car I hope to weld in the cut offs, mostly. The bottom of 1 quarter panel, some in the trunk floor and a few patches in the back wheel wells that won't be seen.
On my Fury it just needs a little work in the lower quarters/ triangles about 3x3 at the lower back edges of the back wheel wells. Not enough to justify replacement quarters even if they could be found. But lots of welded in patches involved.
 
You have a lot of projects to be sure. Sounds like fun though, I'm sure you will figure it out. Grave yard cars on the cable network is a mopar guy, I'd email them perhaps they can give you some advice. They are cutting in parts perhaps there is a process they can suggest.
 
I started the day thinking that I would get my slant 6 assembled until I opened new main bearings and saw a problem within that made me stop until I get another set, came in ant found Stacey David"s Gearz on cable, I occasionally catch it but I found a marathon of the show of sorts on a different channel than I usually watch and got hooked on that for the day.
He gets into a bunch of body work too, along with other fab work he usually shows. I actually thought about sending something to him to ask his opinion, have not done so yet.
 
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