Is this an OK way to reinforce a front sub-frame?

[MoPar~Man]

My plan is to replace the front subframe in my '67 Monaco with this one:

I'm showing here the underside rear passenger side. I would of course clean this frame up and paint it, but I want to go further.

I want to form this out of 3/16 plate steel:

And weld it to the frame:

Here's a shot of the driver-side rear:

The yellow circle is where I think a lift-support is usually placed. On this side, for what-ever reason, that area is some-what pressed in (concave) compared to the same area on the passenger side. Correct me if I'm wrong, but if there was an area on these frames that could use some extra beef, it would be that area.

Aside from a rusty / greasy look, this frame has no rot. If my current frame were in this same exact condition and appearance I wouldn't be touching it.

But since I always want to "make it better", I have this idea that the above-described reinforcement scheme will do what I want.

Or is this not a good way to go?

 

[Owen11x]

You'll wanna leave the section open for your body bolts to go back into but yes it absolutely won't hurt anything. It only helps. Clean it it up. Weld it and por 15 the whole stub

 

[CBODY67]

You'll wanna leave the section open for your body bolts to go back into but yes it absolutely won't hurt anything. It only helps. Clean it it up. Weld it and por 15 the whole stub

As to rust-preventative coatings, be sure to coat INSIDE AND OUTSIDE rather than just the outside! Leave some "drain holes" in the completed structure, too. Remember that "splash" can come from the front and rearward locations, too.

On the stub on our '66 Newport Town Sedan, the original welds were done in segments, for the two original sections of the structure, rather than solid. Initially, I considered that to be "lazy", until our service station tech (a former Chrysler dealership technician) said the segments were actually better than a solid weld. No issues as I later figured out he was correct. The segments would allow for a bit more flex whereas the solid weld could make things stiffer and more brittle. Might also have something to do with the base metal too, as most all of modern pickups now have fully-boxed and welded frames which are stiffer and stronger?

Enjoy!
CBODY67

 

[65Port]

I like the idea but I'd be concerned about moisture getting trapped and causing corrosion on top of the new piece. Just a thought..

 

[Owen11x]

Tip stub on end and dumped each end full of transmission fluid that will keep your moisture out and rust away. It will be fine for your life time unless you drive in the winter and salt

 

[MoPar~Man]

I was going to wire-wheel and use phosphoric acid on all areas of the frame covered by the new piece and then spray that area as well as the facing side of the new piece with Rustoleum cold galvanizing spray paint:

There are weld-through primers for this sort of thing, they are heavy in zinc so I think this will do.

 

[70bigblockdodge]

Sealer all the way around the welded plate, right on the weld. The silicone-latex paintable caulk they sell in hardware stores is perfect, unless you want to spend 3 times as much on actual seam sealer.

 

[Fratzog]

If you enjoy doing that kind of work and a heavier frame is your objective OK I guess. But my question would still be, why would you go to all that effort if all you have is surface rust on the frame? As long as I've had my two old cars the frames have always been cupped front and back from PO jacks but I don't lose any sleep over it. I just make sure to jack at the intersection of frame sections where it is strongest. Also throw a 2x4 in the cradle of your jack stands to distribute the weight a bit. My .02.

 

[polaratherapy]

I did the same on my 67 Newport, not that it needed it , when I went for the safety the mechanic pased it no problem.
He questioned it and when I said lets grind it off and if you can still hoist it you will forgive my invoice, he let it go.

 

[fury fan]

If this replacement sub is rust-free as you say, I would not bother doing this reinforcement to it.
Depending on what your car's body type is, you'd get more benefit tying the F&R subframes together. Time better spent.

As @Fratzog said - just put a block of wood on your floor jack instead.