I had a picture of this crack on my sons truck but can not find in on my hard drive.

The cab does get stressed a lot over the years. Mine when going over a un-even driveway the cab will make a 'BONG' noise when it flexes enough on the frame.

As far as getting a MIG stinger tip in there, I think you could from inside the cab. But I would have someone in the Cowl area holding a 'Copper' backer plate over the crack so you dont just blow through. I have a huge sheet of dead soft pure copper. I just cut a piece and hammer it into the shape I need and hold it under the hole or crack. Check out Mike Finnegan's "Eastwood' Hotrod TV vid on YouTube:

youtube.com/watch?v=huPdLOIA438

Getting into interesting topic. I've been wondering about boxing my frame, at least in spots. Now you have me wondering about the cab. I don't seem to have a leak in cab now, nor really a lot of flex, but thought it would be nice to make it more rigid. Maybe I shouldn't go off on tangent about boxing, etc. though.

Here's your youtube video Dave

https://www.youtube.com/watch?v=huPdLOIA438

yeah it is..... and getting farther reaching than I thought it would. As far as the copper bars, I have a few here, familiar with that trick.

I have an Eastwood store about an hour from me, saw that magnetic one there and thought of getting one while I was last there but the wife was made at me enuf for what I DID spend that day....

good suggestions, keep em coming.... and hopefully those pix of the problem area get "found" so we can all see them....

If you have any intentions of welding in the area of the bottom of the wiper box, I strongly suggest you pull everything out of the interior, the dash, the heater box, wiper parts, the plastic vent boxes, probably the wiring harness, and the carpet off the floor. You really need to get to a bare metal firewall. There is a lot of stuff in that area that will catch fire from the mig welder sparks that will be flying and some of the materials in the area will self feed a fire that may start. The entire seam along the bottom of the wiper box was filled (often very poorly) with a seam sealer from the factory. If you are welding in that area, the seam sealer really needs to be dug out. A fire starting to burn under a dash is in a difficult location to extinguish and would probably cause more damage the the water coming in would. Its not a quick weld job, I've done a few in the past.

While your checking stuff, it might be a really good idea to check the condition of the metal on the frame ear for the body mounts. The rubber mount will hold water and attract dust/dirt/sand and the grit of the dirt will wear away the metal under the mount. The result of that is there really is nothing keeping the cab on the frame, the metal will wear away to the size slightly smaller then the rubber mount. To check this, all you need to do is put a pry bar between the cab and the frame and see if you can pray the two apart. If its good, it shouldn't move, if its bad, the mount will pull right through the frame, any movement more the 1/8" is highly suspect. If your cab is making noises when the the body and frame flex, I would really check those cab mounts, all 4 on the cab, and the 2 at the radiator support.
That hasn't got anything to do with the water leak, other then someone mentioning body/frame flex. That Dodge truck frame and body were designed to flex, up to a point, its the extremes, or the deterioration of the original mounting system, that cause the problems. Gene

Yeah Gene I have seen that and repaired it before. I'm thinking my leak source will probably wind up being somewhere in the corner of the cowl where it wraps around and goes vertical, based on where I am seeing the seepage on the inside of the cab. If all checks out, I'd actually like to put a bird bath hood on to this rig meaning I'd be in that area because I will have to change the vented cowl panel under the wiper arms as those are different with the bird bath hood.
I thought I heard somewhere, that there is an area around that part of the cab that cracked too? I'm hoping that it doesn't wind up being anything to do with the windshield channel area.
Without pulling the windshield strip, what I can see there looks very solid so far.

Oh yeah I think someone mentioned wiper pivot area as a potential leak source? I thought that was just an a body issue?

TSB on cowl cracks:

http://dodgeram.info/tsb/1994/23-63-94.htm


More info:

https://ramchargercentral.com/body-interior/cowl-cracks/

exactly why my trucks have no carpet and spray on bed liner inside & out. also why I moved the dimmer switch to lower edge of dash by hood release. water would short out/rust the switch and it burnt up the fuseable link wires on 2 of my trucks. took a while but I found good replacement wire harness for the 85/88 trucks & moved the switch to high ground.
couple well placed 1/4' holes to drain floors well and it stays dry and a little damp in wet weather but dry's right up dry weather.

IMHO..they all leak no matter what. so drain it well and ride the wheels off before it rust away.

OH yea, windshield gaskets leak also. mine leaked and run water down the a-piller and then down between dash and kick panel to the floor.
cargo light leaked and run down inside cab and keeps seat belt wet and rotting in the bolt area.

Good idea Mike, move the dimmer to high ground, AND I agree, no carpet inside, bed liner inside (I think I'm going to do POR15) and a couple of well placed holes. I have nothing on the floor of mine now, and had posted a question about adhesive backed liners and my concern for moisture getting underneath. I'm eventually going to get a rubber floor and attach the insulation to the back of that so I can easily lift to feel for moisture.

Mike's right, drive the heck out of them after you do your best to protect!

Wow that TSB states "93-and prior"

Just how far prior I wonder?

'72

Okay thanks. Was thinking it might be an '81 to '93 thing.

The '72 to '93 is the same basic cab with a few minor changes.

I know, but was hoping there was some tweaking when the style changed in 81, and that way my '79 was safe from this possible problem.

I see more northern trucks with this issue than the southern ones. Probably has more to do with terrain.

Stealing the picture from that TSB, here is where my son's 74 cab is cracked (Red Arrows)

Its pretty flat around here, only "terrain" issues are bad local roads haha.... now road salt, and that brine crap that they love so much around here, I can see that making a difference, vs non salt belt areas.....

Thanks for posting that.....