I lived in Calif. before being stupid enough to move to Missouri, so I didn't have to deal with rust. My 79 Toyota 4X4 was perfect original paint without any rust.
I was stupid again and sold the 79 when someone offered me a lot of money for it. That was over 20 years ago. So I had no idea that the frames rusted out when I decided to find another 4X4 Toyota about 6 years ago.
My buddy and I made a 3 hour trip one way to look at the one I bought, you just don't see them back here. He told me about the frame rust, so we looked it over good and didn't see any frame rust. The truck has very little rust on it, so I was surprised when it started to drive funny, and I noticed the gap between the bed and cab opening and closing as I accelerated and decelerated.
Climbing under it I noticed some cracks but no big holes. I welded them up and everything was fine for awhile, then the problems started all over again. Eventually I ended up with a real mess. I think the bed and gas tank was what was holding it together.
I had to fix it, so I bought an antique Arc Welder from a coworker. This thing is a beast. We had to use a tractor to load it. I decided on an Arc Welder because it will weld the dirty and rusty metal. My Mig welder didn't want to weld it.
So I pulled it apart, made templates and bought a sheet of metal. I cut the pieces out of the plate with a Plasma cutter, then Arc welded them in. I welded the plates to as much of the original frame as I could. It's really strong now, and everything is square.
The bed will go back on this week. It's been down about 2 weeks, but I haven't worked on it all that much. I probably could have finished it in 3 full days of work.
Here's the pictures,

 

That is some crazy rust. Almost surprised the frame didn't collapse at the rear spring hangers when you hit a bump.

Was that really a wood block between the frame and bed in the 2nd picture? ?

 

No wood block. Just the picture angle I guess.

 

Pretty hard to believe it got that bad and you did not spot it sooner .

 

Frames here in Missouri are either in great shape or rusted out like what you showed. Not much in between. I have seen some that I don't know what kept them from falling apart on the road. Great job on the repair.

 

That's a horrorshow right there. The repairs look crude but effective. What did you do for the insides of the frame rails?

 

wow, I have no idea how you don't notice that in 6yrs of owning. Do you do any prep for winter road driving, like oil spray, Kroil, or whatever you guys use over there?

x2 what did you do to treat the inside and prevent the new steel from rusting out? meh, probably good for another 10yrs, lol.

 

I was surprised how fast the rust appeared. I look the truck over all the time and other than the cracks that first appeared, I didn't see any problems. All that showed up in about 6 months time. Once it started, it just went to crap really fast. As far as prepping the inside, what can you really do? The welding will burn off anything you put on it. So I'll just make sure to keep the inside of the frame clean and hope for the best. I put it back together tonight, and plan on driving it to work tomorrow.

 

I have no idea what you do inside, that's why I asked. Want to know because I need to tackle some rusty A-pillars and rockers on my Oldsmobile and want to make sure it won't come back in a few years after I restore it. I know there are some weld-through paint products and some people spray oil protectants and rust converters up inside cavities too, just was wondering what you did and dang I'm glad I live on the West Coast.

 

You know moving here wasn't a mistake, we had a good reason, but staying here is a mistake. I make at least half of what I'd make in Calif, and it isn't really cheaper to live here. I hope to make my way west again in the next couple of years, maybe Texas, Arizona, or back to Calif.
I wouldn't spray any kind of oil, or silicone, on any part that will be getting painted. Weld through primer would be what I'd use, but it will burn off when you weld, and you still will have bare metal inside. Just fix it and enjoy it for as long as you can. Not many cars where dipped in primer when the where new, some where, but not all. So they had bare metal from day one.

 

Rust sucks.

 

I think the idea with internal frame products is that you apply them *after* any welding happens.

When I was painting my frame (outside only, of course), I had everything off of it, and could hang it nearly vertical from a forklift. I poured a bunch of stuff down the rails: first water, then degreaser mixed with hot water, then more rinsing, more degreaser, more rinsing, compressed air for basic drying, let it sit in the sun for more complete drying... finally some random mix of mostly used oil. It took a couple of days to stop dripping, but a year and a half later, I still see it seeping through the dust around all the holes in the frame.

For touchup, I use an in-bottle pump (like what you use to fill car transmissions and diffs) attached to a hose. Stick a bolt in the end of the hose, and a hose clamp to seal. Cut a few slits with a razorblade just before the end, in a radial pattern. Insert the hose into several holes in the frame, and pump away, pulling the hose back and forth and rotating so as much inside gets coated as possible.

I've heard of good, dedicated products to do this, but used motor oil appears to be an ancient trick, is free, and a lot better than nothing.

 

^That's exactly what I was referring to. DIY and commercial products to do this.

 

I've thought about getting a garden sprayer and filling it with some John Deere chassis black (Blitz Black) and spraying it down inside the frame. I could make the sprayer as long as I wanted to. The Tractor Stores here have a brand of Tractor paint that's really inexpensive, and it holds up well, so I could do that too. I'm thinking about taking the truck off the road this spring and doing the body work and painting it, as well as doing the interior. So that will be the perfect time to do something to the inside, and outside of the frame. If I do that the bed will come back off, and I might pull the cab too.

 

My '81 4x4 frame is showing some signs of impending perforation just ahead of the rear spring front hangers on both sides. Only on the inside plates. We bought the truck new in Alaska where it lived for 15 years, 5 1/2 of those in the bush. I treated the rust that was developing on body panels and living in Idaho has greatly slowed the progress (until they started to use salt on the roads in the winter a couple of years ago), but it is time to do some refurb to the faithful old friend. I'll repair the frame the same way I've done some CJ frames and will post pix when I get started. It has always looked to me like Toyota overheated the steel when welding these frames and burned them, so they rust.

 

I think the frames rust because they're open on both ends, and the center is lower than the front and back, that keeps all the mud and wet gunk stuck in there. The wet gunk will collect in the area in front of the rear spring hangers because the forward motion of the truck will push it there. I'm not sure if the frames where dipped at the factory or not, but the inside is probably bare metal. That's my theory anyway.