84 K30 Cowl Rust

[BlazeOn]

Hello everyone, picked up a real nice 84 K30 crew cab single rear wheel a few weeks ago. As I have been going through it I unfortunately found the only rust spot and it’s a tough one. The cowl seam sealer was cracking out. Today I chunked it all out for the most part. Haven’t wire wheeled or anything yet. All the metal looks decent except one spot. In the curved section of the firewall seam.

I really wasn’t planning on stripping this truck down for any repairs anytime soon. What can I do to fix this with the motor still in.? Needs a 1.5” patch probably. The surrounding metal all looks good so far.

 

[obijuank5]

I am NO expert but I’d use ospho or some rust convertor to stop it from getting worse then spread some thick sealant over it to close the hole up.
Imo that’s terminal cause there’s more where you can’t see.

 

[Blue85]

Even with weld-through primer, the dilemma to a blind patch is that you can't treat the backside of the welds to keep them from rusting. If you can get to the backside, the long-term odds improve. Probably the best way to get in the crack is with media blasting.

 

[Conner]

I think the temporary fix of rust converter, paint on top, and "quarantine" the area with seam sealer would hold it over for a couple years until you can do a permanent fix. I would definitely make sure there are no holes into the cab behind the dash, though. My truck had similar (but worse) cowl rust and there were hidden holes coming into the cab as well as out the front of the firewall at that seam.

When you do permanently fix it, I doubt the backside of the welds would be a problem assuming you prevent moisture from getting to the area by reapplying seam sealer. The alternative (to avoid the "blind patch") is pulling the entire windshield frame panel off the cab, fixing/replacing it, and spot welding it back on. Which is definitely not worth it for damage this mild, in my opinion.

Good luck, if that's the worst of the rust, then you're in pretty good shape I think! And good on you for finding it, most people probably wouldn't even know until water started getting into the cab.

 

[BlazeOn]

Thanks guys. Unless anyone has any reason to say my plan is no good. I’m going to wire wheel the crack a bunch. Clean with shop air and pour Ospho down in there. I’m going to cut the hole to clean metal. I’ll pour rust converter primer after the Ospho and then a shot of epoxy. I’ll use some hvac aluminum tape to cover the hole to keep the shape and then fill with seam sealer. Then I’ll take the tape off maybe.

Probably pull the cowl in a year or two to fix it correctly but my k5 is midway through it’s restoration and it stuck in the shop.

 

[obijuank5]

How are you getting in there? I didn’t know you could get tool access in there.

 

[BlazeOn]

How are you getting in there? I didn’t know you could get tool access in there.

Just removed all the covers and plastic grate. Using a small die grinder with a wire wheel attached.

 

[obijuank5]

Just removed all the covers and plastic grate. Using a small die grinder with a wire wheel attached.

Right I can see that. I remember it being pretty tight when I was in there last. Probably not bad with the right tools.

 

[BlazeOn]

Right I can see that. I remember it being pretty tight when I was in there last. Probably not bad with the right tools.

Oh it’s definitely not comfortable in there but I’ll try to grab some pics along the way

 

[BlazeOn]

Got it all cleaned out. So far just that original hole. Cleaned it up and it’s back to good metal. Overall about 1.5 inches oval hole. The rest looks pretty good. I’m going to treat it several times with ospho and go from there

 

[Conner]

That's not bad at all! Any chance you can get to it for a patch if you pull off the air cleaner and carb? I'd be tempted to just fix it for good really quick if possible to cross it off the list, but that's just me. Then you can seam seal it all once and forget about it for another 41 years