Rustproofing idea: airtight frame?
 

1. Put frame on rotisserie. Pressurewash the inside with diluted degreaser, get it as clean as possible, dry thoroughly.

2. Weld up or otherwise permanently seal all the small, useless holes in the frame.

3. Make some bolt-on covers for the remaining bigger holes, with rubber gaskets. Rig up an air fitting to test the whole thing for airtightness until it passes. Assume that airtight means water- and other-crud- tight.

4. Throw in some light oil, turn the frame every which way to spread it around. Add a few dessicant packets here and there, and bolt the covers on. They're there in case I ever need to get back inside the frame to check/add oil, change the packets, inspect, whatever. Probably won't open them more than once or twice in the truck's lifetime.

Thoughts? I've heard of all kinds of oils, waxes, sealers, whatever, sprayed inside frames to keep them from rusting. Is there a reason nobody's ever tried to seal it up so it's air- and water-tight like this?

Sounds good. I think the biggest drawback to a sealed metal chamber is the moisture that accumulates inside can't get out. And after a while no matter what kind of oil or moisture absorbers you put in there it will start to rust. Plus if you totally seal it, it will have pressure or vacuum depending on the temp outside. If its hot it could have as much as a couple psi inside, if cold it would have a slight vacuum. Now I'm not sure about vacuum causing any problems, but pressure on the other hand, well if you don't drain your air compressor it rusts in there pretty bad, and real quick.

Good point, but I thought of that, and that's why I'd add silica packets (the "DO NOT EAT" little white baggies in snack food packaging) to remove all moisture. Think that'll fix it?

Pressure, huh? Hm... once idea would be to beef up the covers, and actually test them with, say, 20psi above atmospheric. Other idea is to keep the air fitting, and pump some or all the air out, leaving it at a partial vacuum to allow for heat-related expansion.

Ya not sure, but I think vacuum actually helps with moisture. As not to condensat inside to begin with.

Oh... forgot to say, I wish there wasn't so many holes in the frame to begin with. Those square ones let in a lot of dirt and debris.

So if it was at a vacuum to begin with it may never become pressurized.

If you look at your frame, there are holes on the underside and inside of the frame rails. This is to allow moisture to excape and air to dry the inside of the frame. I would want to keep those insted of pluging them up.

I do see what your trying to do to create a seal and therefore not let any water in, however frames are not designed to act as sealed beams or they would have come from the factory that way. I think you would be inadvertly rusting your frame from the inside out.

Air flow is your friend, the more the better...

Why are there so many small holes? What do they do? The big ones, fine, they're for some kinda access. But all the 1/2" and smaller ones, especially on the frame right behind the cab - why?

Actually, my frame has no holes on the bottom whatsoever. If I abort this idea for whatever reason, I'm going to look into drilling some for drainage.

Yup, that's the idea. I'd only vacuum it as much as it could conceivably expand under temperature, the reasoning being that too much vacuum and it might be more susceptible to damage (think plastic bottle crushed by sucking the air out, except less drastic).

Corollary idea: seal it up except for one or two holes, and run vent hoses up to the cab, sort of like how axle housings are vented.

That would take care of any pressure related problems.


Also most rusted frame cases I've seen it didn't appear to have originated inside the frame, but more outer. I could be wrong in my assumption, but thats what they look like.

You know, I'm wondering - so what if I drive through Death Valley one day and my rubber gaskets vent off a few psi at the seams? Unless they actually rupture, they'll seal right back up and I'll be at a slight vacuum when the truck cools off. How is this a problem?

That's completely opposite from everything on frame rust problems I've ever read...

In any case, internal rustproofing is pretty much a separate project from the outside of the frame. The difference is that the outside is much easier to touch up or completely redo later in life.

Many holes are there so the robots in the factory can hold and move the frame. They're left open because it would greatly inconvenience the manufacturer and add cost to seal them, and it's not much of a selling point to the new car buyer. Some have lines and cables going through which would require rerouting.

I think it's a lot of work but a good idea. The windows in your house are sealed with dessicant and last for decades until the silicone breaks down and lets moisture in. Go totally sealed if you do it though. Vent lines will just let the dessicant fill up and defeat the purpose. BTW, compressors fill up with water because they take say 50 volumes of ambient air and compress it to one volume, so you have 50 times the amount of water. If you take a tank, dry out the air inside with dessicant and seal it, it can expand and contract indefinitely. No moisture is going to form in there simply because it is under pressure. I think a frame under pressure would be stronger and safer than one under vacuum.

Also... Consider giving it a shakeup with some watered down phosphoric acid before drying and oiling, should eliminate any existing rust in there.

Not that I really think that the slight amount of vacum that could be created would cause a problem but here is a cool video of what happens when hot air is trapped in something and then gets cold. Just something to think about.

Tank Car Implosion

Since you have the frame stripped down to the point you can rotate it, why not take a coating material and pour down into it to seal up the metal inside. Something similar to what is used for gas tanks that are rusty.

If you can get in a really low humidity room, use the sealer and then close up the holes, that might work.

Probably be very hard to seal the frame up. It is really not a welded box tube, rather it is a pair of facing C-channels that are spot welded on the top and bottom. One option I've heard of is getting the frame hot-dipped galvanized. If you could get the inside of the frame coated with molten zinc, that would probably be the best you could do.

I hear that. This whole idea was inspired by looking at 1. the insides of axle housings, and 2. the insides of rocker panels that don't have any rust holes. The former has oil and vents, and I've never seen a rusty one. The latter is more or less airtight - spotwelds and a rubber plug or two - and has negligible to no corrosion in the ones I've seen. I'm trying to replicate one of these two scenarios with the whole frame.

I haven't figured out the exact details of the cleaning step, but that sounds like a good idea.

:laugh: Cool! That effect, at a much smaller magnitude, is something I'd like to avoid. So no vacuum frame for me.

Excellent question. The reason I'm disinclined to just spray Eastwood's frame spray or Corroseal or Nikawax or Mike Sander's whatever is that I don't trust the longevity of any of those products. I hear lots of reports of people happy with their initial appearance of durability, but few long-term reviews. If I spray something in there that turns out to crack and collect moisture after 5 years, I'm going to be mighty pissed when it's inside the frame and impossible to remove. Outside of the frame, I'm more willing to experiment.

Too expensive. My time is worth a lot less than my money, and I'm willing (at least, for now) to keep doing spotchecks with an air compressor until the whole thing is airtight.

Another inspiration for this idea is someone on here (I forget who) who built a flatbed on their 3rd gen out of square tubing, and made it airtight enough to be a compressed air tank. Didn't sound that hard to get it tight.

From air pressure changes, or do you mean something else?

I think if I go through with this, I'm going to install some kind of humidity gauge, and maybe some kind of fine-scale air pressure gauge, to monitor how tight the frame stays over time.

seems like you are way overthinking something that proven solutions are readily available for...JMO

Amen!.
After all that that water-proofing process, you would have already spent too much. Might as well make a custom frame out of stainless steel. =D

Well, I wouldn't be welding *every* hole shut, I'd leave a few with bolt-on covers in case I ever need to get back in there for some reason - to check on the oil or dessicant or its general state, or to equalize pressure with atmospheric if I ever move to the Dead Sea, for instance.

If a flatbed can be made into a compressed air tank, I can't imagine that a frame, with thicker plate, would suffer from being a few psi overpressurized.

Sounds like a total waste of time to me. I would just slosh some POR15 around inside the rails and coat the outside.

No way. I used POR15 on my last project. Without adequate prep it's not only ineffective, but the parts painted without prep rusted before everything else did, like the stuff peeled and trapped moisture more than the semi-raw steel underneath.

Why isn't there a real paint? Something that actually eats into the steel. Something thats actually dangerous to handle wet. You ask me all these paints we have are safer then sorry POS's. Its just like those scissors for kids, their safe but they don't cut worth a ----.
I want a paint that I actually have to be carfull with. That would be nice.

But I really don't think turning your frame into an outerspace environment simulater is the answer either.

Come on man!! Gauges to monitor the pressure and humidity for the frame of your truck? Your asking for failure. Don't build a vehicle that relies on constant human attention to remain stable. These trucks can sit in a farmers field for decades and be revived. Yours is require the attention of a nuclear power plant when your all done and is still gonna rust :(