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.

 

[MoPar~Man]

So here's what I ended up doing. First, I wasn't liking how this part of the driver's side rail bottom had pancaked:

The other side was essentially in perfect condition. But I hate that they used such thin metal for these frames. So instead of my original U-shaped design to weld over this, I went just for a flat plate:

3/16 is really tough to bend!

Now it's ready to be put on a lift! Time for the other side:

Each piece weighs 7.25 lbs. If I can find a place to do it, I'm going to get this powder coated, along with the upper and lower control arms.

 

[CBODY67]

Those plates make things look really nice. Please keep us posted on any changes in handling behavior, ride harshness, and general feel.

CBODY67

 

[fury fan]

Ordinarily when welding a sealed cavity like this one should make some drain holes, as condensation happens whether we drive our cars or keep them perfectly dry.
If the original frame plate rots out, so be it.
And the 3/16" will take a long time to rust thru.
But - the weld seam areas at the bottom of the framerail might be the next vulnerable area to check periodically.

 

[CBODY67]

The weld seam on our '66 Newport looks kind of sloppy to me. Segmented welds, not solid. No issue with draining moisture as it's all open. I questioned the segments, rather than being solid, and our trusted mechanic claimed it was better/stronger that way.

CBODY67

 

[MoPar~Man]

From what I could tell, and I went over the entire frame with various rotating abrasive appliances, the entire length of the 2 segments of each rail are welded with a continuous weld, the weld being somewhat variable consistency. Two U-shaped pieces joined side-by-side, welded in a long seam top and bottom. I removed some excess slag in some places, and touched up some welds on other joints.

I coated the surfaces that I sealed up with the plate with a zinc paint, I won't be drilling any holes in the new plate - that would garantee them getting filled with water from road splash. The frame is being epoxy powder coated now, along with the upper control arms. Lower arms will be next (I welded a reinforcement plate to them).

Thinking of getting my new tank expoxy coated (on the outside) - maybe in a silver or light grey? Keep it metalic-looking?

 

[MoPar~Man]

I'm wondering how to support the car during stub frame removal. I've seen several threads on FCBO and can see the stands in pictures but not from the vantage point showing where they contact the underside of the body. The service manual says this: "The floor stands should be placed under the rear axle and under forward edge of floor sills."

They mean the underside of the rocker panels?

In this diagram, do they mean the area in the red circle? Would the area in the blue circle be better? Or perhaps distributed over both?

A 2x4 is wide enough to sit under the sill/rocker panel in those locations - yes?

Also - the drive shaft (propeller shaft) will just slide out of the transmission when the stub-with-engine+trans is rolled forward - yes?

 

[fury fan]

Take the driveshaft out first, don't risk damaging your output shaft bushing or seal. It's only 4 bolts. Good time to check your U-joints anyway.
Personally, I would run a 4x4 post or something similar side-side, a bit wider than the car, and put jackstands under that.
You'll need to space downward a bit, as IIRC the subframe hangs a little lower than the rockerpanel pinchweld, so put the stands wherever you have solid blocking from garage floor to rockerpanel.

 

[MoPar~Man]

The lowest point under the car from what I can see is the vertical seam that runs inboard along the bottom of the rocker panel. If you put a wood beam side to side, the weight of the car lands on that seam and it will get folded and the weight will settle on the rocker panels. If there is any part of the floor lower than the rocker panels, I doubt they're stong enough to not get punctured or mangled. Where-ever you put a support stand, it can't interfere with pulling the stub forward once it's been unbolted. Which means it has to be to the right of the blue circle on the diagram.

 

[CBODY67]

When my former workplace was an AMC-Jeep-Renault dealer for about 6 months in the early 1980s, one of the "required tools" we received were 4 wooden pucks, about 6" in diameter, with a groove in the top of each one, about .4" wide, for lifting the car on the rocker panel pinchweld area. The groove was where the pinchweld went as the rest of the puck touched the rocker panel itself.

I was considering buying a Fuego, which the pucks were for, but I decided that if it took those special tools to just jack it up. no deal for me.

Perhaps something of that nature might work in your situation?

CBODY67

 

[MoPar~Man]

This is how I have it supported:

I really don't see any other place to support the car and allow the stub to be pulled forward without interference. Once the stub is out I can put additional jacks under the car where the outriggers were attached. Right now the tires are still touching the ground barely so most of the weight is on these blocks. Seems solid there. I was going to arrange the cinder block lengthwise and use longer planks but they get in the way of the frame bolts I need to reach.