Roof rust under weather stripping

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Masterb4tes

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Hi guys,
So I have finally started looking at my 97 GMC Sierra, cataloguing all the things that need doing to it at a minimum and lo and behold... Rust. There is a little in the floor, which I am not too concerned about, but the rust building on the roof has me worried. Now I am located in Australia, which means parts and donor vehicles are limited if not non-existent. So I ask the brain trust here, how worried should I be? And what course of action would some of you take?
 

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GrimsterGMC

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You want to get onto that real quick, luckily we are coming into Summer so it can dry out. You will have to take the roof liner out as will be on the inside as well since there are holes already. Wire brush the hell out of it and remove as much of the oxide as you can then brush Hydrochloric acid over the holes. It dissolves iron oxide on contact but leaves clean steel alone, then flush out with water and see what it looks like. You may be lucky enough to get away with a couple of small patches welded in but lay a wet towel along the edge of the roof to keep any heat away or it will start to wave and that will be a whole other problem. Take your time and it will come out fine. Out of curiosity, did it have a roof rack on at some time that caused this?
 

Masterb4tes

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No roof rack that I am aware of @GrimsterGMC, just gunk and such stuck in the outer weather strip. I also believe it spent a fair bit of time outside in the heat and rain.

Rightio, so what you are suggesting is pretty much where my mind was heading, but I am not a panel guy so I am totally open to advice. This rig is not on the road at the moment and I am trying to decide what I will do with it, will I just do the minimum and get it on the road, or should I throw time, effort and money at it. I'll maybe take out the liner tomorrow and get a better idea.
 

bretcopsey

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Something to consider-instead of welding in a patch, perhaps use a panel bond adhesive to patch from the inside after cutting out the rust. Then filler, prime and paint or skip the filler since the patch wouldn’t be visible when the door is closed.
 

Masterb4tes

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@letitsnow The climate in Far North Queensland is very harsh in terms of heat and UV damage to vehicles, plus we get monsoonal rain. Unlike a lot of US trucks this thing has no chassis corrosion, no issues in the rockers or the cab corners. Unfortunately for me, rust is one of the few things I am not well equipped to deal with...
 

Hipster

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The area it's rusted is the seam where the roof overlaps the door opening frame. It really needs patches welded in , seam sealer etc. Panel bond as a filler is not really a solution for properly plug welded flange. Really have to start cutting before you can determine how far the rust goes and what would be the best way to patch it. Might be easier to go from cab corner almost to hole in the door frame with one patch instead of multiple pieces. Plug welds along the side on the door frame and welded along the roof line via small tacks(skipping around) until it's a solid bead.
 
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letitsnow

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@letitsnow The climate in Far North Queensland is very harsh in terms of heat and UV damage to vehicles, plus we get monsoonal rain. Unlike a lot of US trucks this thing has no chassis corrosion, no issues in the rockers or the cab corners. Unfortunately for me, rust is one of the few things I am not well equipped to deal with...

I see. Hopefully it is just a small area that had some sort of manufacturing flaw, causing it to rust in only that area.
 

bretcopsey

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Panel bond as a filler is not really a solution for properly plug welded flange. Really have to start cutting before you can determine how far the rust goes and what would be the best way to patch it.
Not disagreeing-just wanting to clarify that what I meant was cut out the rust, make a sheetmetal patch that will fill the hole from the inside plus having enough overlap to then use panel bond to attach from inside the cab. I am not intimately familiar with the construction of that area if it is a possible solution, but could be a way to avoid welding.
 

Masterb4tes

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Oh so I have the roof liner out and it looks as if the interior is still sound... It is rusting from the outside. I'll start by wire wheeling and maybe flap discing the area and see how much material comes off....
I reckon the outer weather seal was full of dirt and salt etc and the sitting water and material has compromised the overlap seam.

@Hipster Do you think I can use flat material to do the patch pieces or will I need something moulded? I know where I can get cab corners and floor pans but I havent seen any sort of roof panel in Australia.
 

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