1972 Cab Joint
Fleet Mechanic
Joined: Aug 2007
Posts: 1,839
Likes: 263
From: Piney Woods of East Texas
It's seam sealer. The bigger problem is that water gets in between the joint and rusts. The best fix it to weld up the seam. You need to dig out all of the old seam sealer in order to do any repair. Time consuming process. The newer sealants are much better these days.
More Turbo
Joined: Feb 2001
Posts: 527
Likes: 80
Hit that seam with a small wire brush til it looks cleaned out. Then spray in / brush in a good amount of Rustoleum Rusty Metal Primer. If you want to wipe off overspray, a rag with lacquer thinner etc., will clean it up the way you want it. But leave the primer IN the seam.
This is the best I’ve come up with for treating those seams.
This is the best I’ve come up with for treating those seams.
More Turbo
Joined: Feb 2001
Posts: 527
Likes: 80
The Rusty metal primer is outstanding for not allowing moisture to penetrate. I’ve used it on these seams, also the long one on the rear cab roof over the back window, and the front of the hood. I apply a thick coating of this stuff into the seam AFTER the seam is cleaned out. No oily residue or other material. Pick out all the small scales of rust. It’s going to adhere to clean surface rust.
I’ve also used it successfully on just plain surface rust that I wanted to cover and stop the progression of the rust.
Multiple coats will be best, let it dry for a few days, apply some more. I keep it confined to just the seams by wiping off the overspray with thinner or acetone. This did a good job on my seams here in rainy Washington where the truck is outside all year.
If you eventually painted the truck I’d guess you’d need a sealer coat over everything.
IMO trying to weld up the seams is a can of worms. Warping, trying to weld rust…
It won’t work on the bed seams as there’s too much moisture coming in from the back sides.
I’ve also used it successfully on just plain surface rust that I wanted to cover and stop the progression of the rust.
Multiple coats will be best, let it dry for a few days, apply some more. I keep it confined to just the seams by wiping off the overspray with thinner or acetone. This did a good job on my seams here in rainy Washington where the truck is outside all year.
If you eventually painted the truck I’d guess you’d need a sealer coat over everything.
IMO trying to weld up the seams is a can of worms. Warping, trying to weld rust…
It won’t work on the bed seams as there’s too much moisture coming in from the back sides.
Last edited by jzjames; Feb 27, 2026 at 10:47 PM.
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