Frame Fixin' (looking for advice on welding to re-enforce rust-points)

Happy Sunday!

So ol' Jolene and I are getting along great. I finally have the axle mostly worked out, I rebuilt the drive shaft, the rear brakes are fully restored, and now I'm working on addressing some rust points. You can see in the pictures below that I've isolated most of them (I'll get to the leaf spring mount in a second), and now I just need to figure out exactly what I want to do about them.

My current thought is to get a mobile welder in here and to weld 1/8" plates (pretty sure that's the original gauge of the steel frame...) over each of the rust points but I know there is a discussion on exactly how to go about doing this and I'm also unclear on what to do AFTER that. Looking further, past this part, I need to treat it to help prevent future rust on the frame. Currently I have a few thoughts. Remove the rest of the rubber coating that the last owner put on it and use rust reformer as a primer THEN rubber coat again, or maybe some form of engine enamel? The POR15 just isn't an option because this project lives outside (no garage to work with) and I don't have the facilities for a full frame-off breakdown and refurbishment - basically I'll end up doing everything BUT that while leaving the cab on.

So anyway, if I weld plates over the rust-points how do I treat the spots under the plates, or revent moisture from getting in there? Just not sure what to do about that.

The final piece of this is what to do about the leaf springs? I'm probably going to have to remove one of the mounts (pictured below) to re-enforce the frame where the rust point has broken through. This truck is nearly 40 years old. Should I just go ahead and replace the leaf springs and mount brackets entirely? Taking all thoughts on this matter as I'm in a little bit of analysis paralysis.

As always thanks for everyone's help!

Jon - See if TSB 90-13-9 Frame Cracking At Rear Shock Mount doesn't help.  And in particular see Step 6: Weld Repair Guide.

However, your frame is rusted out instead of cracked, so you might consider a slightly different approach.  You could put a copper plate behind the hole in the frame and then fill the hole with weld and grind that back smooth.

As for treating the metal, I'd paint the frame and the plate with weld-through primer, like shown here.

I would change the shock mounts and rear shackle hangers as a matter of course.
I have used Dorman parts on my truck and so far they are working out well.

I doubt the shock mount would care about the extra thickness of a plate but you might consider cutting out a lozenge shaped piece of frame rail and welding it in flush so it doesn't affect how your truck tracks.

Rubberized asphalt undercoating is disaster for cars. It just traps moisture and brine in against the steel.
Scrape it off (if you can) and use a wax/oil mixture like Fluidfilm or do like the old-timers and lather it up with your old oil change.

I've had to fix these same holes, and replace all of the shock mounts and leaf spring hangers. I usually cut the bad spot out completely, and weld in a new piece, then grind flush. That way it doesn't look repaired...it just looks normal.

The only time I've welded plates on top of the frame surface was to toughen up weak areas (had become thinner due to rust). For the rear spring rear hangers, I plated the frame on the inside when I bolted on the new rear hangers. I basically made large square washers (maybe 2"x2") and after bolting on the hangers, welded the square plates to the frame.

Oh man do I remember those rust holes...those upper shock mounts were such a bad design. The changed the frames later on so that there was a space behind those upper shock mounts. Not sure when they did then, but probably 1992...

I fully intent to remove the rubberized coating but the issue is, I'm down to either bare metal or brown metal (that's just coated with a layer of rust I can't just brush off). So the question then becomes, how do I seal it without going full-on frame-off restoration and doing the whole POR15 treatment.

I think I will end up welding plates over the spots in question, and then welding in the hole, but when I'm done, what is the best way forward to sealing the frame of naked metal? I feel like just oiling up the frame of naked metal is a little risky.

It's WAY better to have rust exposed than sitting wet behind peeling undercoating.

Ospho (or another phosphoric treatment like SEM's Rust Mort or Kleen-Strip Concrete and Metal Prep) and good old Rust-Oleum (or tractor & implement paint) in the sheen of your choice.

Then be sure to apply a wax/oil (not cavity wax) or straight oil to anything that offers a pocket, seam or corner.
You want it to get in there so water can't.

I am a BIG fan of Ospho/Phosphoric acid as a pretreat.  I used it EVERYWHERE on the body and the frame.

One caution for it is you are using it, say, on the body--some epoxy paint will not etch/seal.  So you have to neutralize the acid, but do not delay in setting down the primer after neutralizing.

yeah I'm hearing a lot about Ospho. If I do apply that, sounds like I'd need to neutralize it before priming it and painting no matter what? Right? In that case, what's the correct agent after it and then what is a good primer to go with.

Man, this is quickly turning into a frame-off restoration.

You don't really need to 'neutralize' it.
The whole point is that it etches and converts iron oxide to iron phosphate, so you don't want to go after it with sodium bicarbonate or something.
Just rinse it off well with water and if you have a compressor blow out any moisture in seams and laps.
I typically use an acid etch epoxy primer, but you can go right over the blackened phosphate layer with any DTM industrial enamel.
This is considered 'best practices' for plant maintenance and exterior ironwork.

Another thumbs up here for Ospho! Man I love that stuff, and we get all the rust here...same as all the worst US states from Michigan to Upstate NY and New England.

I have done a couple rusty Bullnose frames with Ospho, but also brake drums and other odds and ends. I think the stuff is brilliant!

Remember that Ospho was just a Dupont trade name for the product, just like Lucite for acrylic sheet or Lexan for polycarbonate was before they sold them off.

Kleen-Strip is the same green liquid for 1/2 the price (and a little goes a long way when diluted)
Plus it should be available at the big orange box nationwide.