Suggestions on Torque box protection?

So I just finished rebuilding both torque boxes. Not fun. Not the worst thing ever, but not how I like to spend my garage time. I painted all the interior surfaces I could before welding them up, but obviously some of the paint had to be removed for welding.
I was brainstorming ways to prevent them from rusting in the future by keeping water/debris out. So any ideas? The only thing I've thought of, and this sounds like a bad idea in my head but could spur some thought, is expanding foam. There's the drainage hole in the bottom (more like the let everything on the road in hole) that could be used to fill it. In theory filling them would prevent crap from getting inside from any of the 7 or so seams. Or, the foam could trap water and make it worse, I don't know much about that stuff.
Any thoughts? Better ideas?

Also, I've considered welding in a piece of plate across the torque box to link the rocker and inner frame rail. The idea is to protect, reinforce, and act as a jacking point. I've been told this could prevent the boxes from caving in a front end collision, but any other downsides I'm missing?

 

when we make and install torque boxes we wait until after they are welded in place and then spray the insides with as much undercoating as we can through the drain hole. Then we put a rubber plug in the hole to seal it. We have not had one rot back out again yet.

 

That was another idea I considered. Any recommendations on brand for undercoating? Eastwood has some stuff thats made to be sprayed inside frame rails, but I'm not sure how it would work since I've already painted inside.

 

Also you could have coated everything with weld-through primer before welding.

 

That's exactly what I've seen happen when foam was sprayed into places like that, it acts like a spnge.

 

Dont use spray foam!!! It will help the boxes rot away. Spray some form of undercoat inside em. I havent tried the Eastwood spray stuff yet but it looks promising. You may want to try it out...It cant hurt. You could also seal all the seams/joints with seam sealer, but then you have to make certain moisture/water will never enter the boxes since it will never be able to drain out...Good luck!!!

 

I tried that, and I'm convinced that weld through primer is a lie. Welding through it sucked. Also, I thought that primer needed topcoated to prevent it from absorbing water?

 

I plan on seam sealing from the floorboard side. I'm afraid of sealin the entire box without knowing that its extemely well protected for exactly that reason.

 

Do you really think it would rot out again? It's not like your car will be subjected to the weather, like it was when it was just an everyday car. Plus, the metal you used, is likely much better, than what was used when the car was built.

 

Me and about a million other people don't have a problem welding through it. Weld-through primer is 90-something percent zinc to make it conductive, applied to properly cleaned metal it holds up very well on it's own. Very similar to cold galvanizing.

 

Hmmm, must've been operator error than. I just didn't seem to get a good arc off the metal with the primer on it. I'm new to welding though, so it's probably something I did.

 

You're probably right, I just tend to do things to the point of overkill. The good news is that is that now every speck of rust is gone from my floorboards with new steel welded in and a fresh coat of paint to keep it from happening again.

Any opinions on adding the plate to the bottom of the torque boxes anybody? The main motivation is a good solid secure jacking/jack stand point. I'm thinking just a piece of diamond plate welded across the flat portion from rocker to frame rail. I'm doing the same thing to the front crossmember where the struts attach. It was curbed hard at some point in its life and even after pounding out the worst of the dents its still ugly and difficult to get jack stands evenly loaded on.

 

3M also makes a spray, similar to Eastwoods, that is used on the inside of body panels to protect them. I have shot that on the insides of my frame rails after popping those floor plugs out. It goes on thick and seems to stay a bit pliable. I got it from my local body work supply shop.

 

I just take some used engine oil and spray it all around inside. I use a 1 gallon pump sprayer from Walmart. The oil will soak into all the seams and prevent rust from starting there! It works great in the bottoms of doors too! Just stick a piece of old cardboard under where you're going to spray,and it'll catch what oil runs out.

 

The trick to preventing corrosion is not allowing the oxidation process to start to begin with. If you sealed the metal surfaces well and coated with seam sealer where it might seep in between panels, you should be fine. Water sitting on these surfaces over a period of time is what rots the metal(and the fact that these cars are made of crappy metal) so just coat everything well and make sure water can drain from everywhere. I personally wouldn't plug any drain holes or access holes for fear of trapping water that may make it's way inside, especially the torque boxes. Metal prep and coating is the key.