Cowl/Firewall/Floorboard rust

[parzan]

greetings.

I just purchased an 84 SWB which I thought had minimal rust. However, after some rain, I discovered water on the floorboards and after some investigating tracked the leak down to the cowl seal.

You can see in this pic that the sealant has failed and there are a few small holes allowing water into the cab.

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There is also a hole in the firewall close to where the evaporator lives. It looks like water would flow down the firewall, get trapped in the insulation, and then... rust.

Here is the firewall hole:

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The floors and the bottoms on the kick panels are rusted also. I haven't taken a wire wheel to them yet, but I think they are solid enough to salvage.

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I plan on taking a wire wheel to the cowl area and then using POR15 on it, and then replacing the seam sealer. But, I'm not sure what to use to seal the holes. Also, what is best product to use for the seam sealer?

Any suggestions on the firewall hole? I don't have a welder and have never welded before. Would using POR15 on it and then patching with fiberglass work?

For the floors I again plan on using POR15 products. I noticed they have a kit for floor pans that I'll take a look at.

Any thoughts or suggestions?

Thanks.

 

[Charlie]

 

[legopnuematic]

In my opinion welding new metal in is the right and proper way to repair rust. Fiberglassing over rust might work for a while but will most likely retain more moisture and rust even worse while being hidden.

On my rust bucket of a 79 have been cutting out the bad and making new patches and welding them in. Here is one for the floor board to the firewall.

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Made patches for the cab supports, braced, new kick panels in progress, have yet to patch the piece above the kick panel.

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More of the firewall rust that needs to be fixed

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All of the work I have done has been done with the $100 harbor freight welder. I'd recommend either finding a friend who can weld and teach you and borrow their welder, have a friend weld it, or take a class at a community college for welding and then shell out the money for one.

 

[parzan]

I plan on heading to Harbor Freight tomorrow. I'll check the welder out. I have a feeling the floors will need some patching or replacing also and it'll probably be a good tool to have in the garage.

Luckily I think this is the only rust the truck has unless I luck out and find more. I thought I looked it over close enough, but obviously missed a few things.

Thanks for the suggestions.

 

[parzan]

legopnuematic,

Did you get the flux welder (I think its either 90 or 125) from Harbor Freight?

Thanks,
Chris

 

[da_raabi]

legopnuematic,

Did you get the flux welder (I think its either 90 or 125) from Harbor Freight?

Thanks,
Chris

That is what i used to completely replace the floors on my Camaro. It's not the best welder in the world, but it will get the job done. Definitely practice first. Being a flux-core welder it makes a LOT of splatter/mess. Expect to do a lot of grinding. Like I say though, it gets the job done.

 

[parzan]

That is what i used to completely replace the floors on my Camaro. It's not the best welder in the world, but it will get the job done. Definitely practice first. Being a flux-core welder it makes a LOT of splatter/mess. Expect to do a lot of grinding. Like I say though, it gets the job done.

Thanks for the info, appreciate it!

 

[peats]

maybe buy a better welder. is this your first build? through the years i always relied on someone to weld after i had done the tedious work of cutting and fitting the new metal in. then about 10 years ago i bought a miller 140 auto set, great move. easy to learn mig and you don't have to rely or pay someone else any more. you can probably find a nice unit in the 400-700 dollar range and will last a lifetime. no longer at the mercy of someone else. as for the cowl and floorpan i had similar issues on my '81 c10 short step.. i cleaned all of the old seam sealer out of the cowl, rust encapsulated the metal, laid 2 layers of fiberglass in the seam and then topped it with 2 layers of bed liner. i have used por-15 several times as well and it is a great product if applied properly. follow the instructions carefully and don't skip the phosphate cleaning/coating step. my guess is after you start beating on the floorpans they will be too far gone for a por-15 fix.

 

[parzan]

How bad was the rust in your cowl area? I haven't started to clean it out yet but I'm concerned it may be worse than I thought. I'm seeing a few more holes now that I'm taking a harder look at it. It's out of the weather, so luckily no concerns of water entering the cab.

Can you elaborate on what fiberglass product and bed liner you used?

Thanks for the help.

maybe buy a better welder. is this your first build? through the years i always relied on someone to weld after i had done the tedious work of cutting and fitting the new metal in. then about 10 years ago i bought a miller 140 auto set, great move. easy to learn mig and you don't have to rely or pay someone else any more. you can probably find a nice unit in the 400-700 dollar range and will last a lifetime. no longer at the mercy of someone else. as for the cowl and floorpan i had similar issues on my '81 c10 short step.. i cleaned all of the old seam sealer out of the cowl, rust encapsulated the metal, laid 2 layers of fiberglass in the seam and then topped it with 2 layers of bed liner. i have used por-15 several times as well and it is a great product if applied properly. follow the instructions carefully and don't skip the phosphate cleaning/coating step. my guess is after you start beating on the floorpans they will be too far gone for a por-15 fix.

 

[da_raabi]

I did a similar process when I chased down a water leak in the cab.

I kept getting water coming in up around the brake pedal and finally realized it was coming down between the two sheets of metal that make the firewall, then entering the cab through the brake pedal holes. I pulled the cowl off, stripped out the old seam sealer, and re-sealed with SEM seam sealer. The metal was in good shape underneath so I think I caught the problem early enough. No issues since. Now I just get water coming in from the stupid a/m sunroof. That will be going the way of the dodo bird ASAP!!

I did not go through the longer process outlined above, I figured seam sealer lasted for 30 years, this stuff should last another 30!

 

[curbstone mech]

I'll be using a good bit of seam sealer also. Especially on top of my welds that are exposed like the inner rockers,etc.

 

[charlesg]

Thanks for this thread, I have a little leak and now a place to look for it, it is up by the firewall so I will check out that seam seal!!!

 

[Jrgunn5150]

I'll just say this, by the time you buy a welder, all the cut off wheels, wire, etc etc... Patch panels, on and on...

You could even take a long road trip and get a rust free cab. I've patched my cab, and I won't do it again.

All that said, just buy whatever welder you can afford and get to work. Cheap welders work fine. If you can afford a better one, that works fine too. The only real difference is flux core vs MIG, and then the bottle and everything add's a significant cost on top of the 400 or whatever you spend to buy the machine in the first place.

 

[4WDKC]

I'll just say this, by the time you buy a welder, all the cut off wheels, wire, etc etc... Patch panels, on and on...

You could even take a long road trip and get a rust free cab. I've patched my cab, and I won't do it again.

All that said, just buy whatever welder you can afford and get to work. Cheap welders work fine. If you can afford a better one, that works fine too. The only real difference is flux core vs MIG, and then the bottle and everything add's a significant cost on top of the 400 or whatever you spend to buy the machine in the first place.

Dont forget you also need to dig out the sealer in the replacement cab and reapply to keep it from drying and rusting out like the old cab.

 

[parzan]

Maybe I'm being too optimistic, but I didn't think the rust was anywhere near needing a cab replacement. I hope I'm right.