Hello All. Stopped by my cousins yesterday to have a closer look at the frame rot. I pulled the front (drivers) wheel and borrowed his angle grinder with a wire wheel on it. After digging around in there I'm curious to know if anyone has cut into one of these subframes and can tell me exactly how AMC put them together. I looks to me that the subframe can best be described as several pieces of c-channel that have been welded together but with an opening on one side. Instead of the subframe being one continuous piece, it looks as if it is made up of several pieces of c-channel, some horizontal and some added in at an angle, and then covered with a stamped piece of metal that gives it that nice curved one-piece look. The subframe appears to had then been covered with Ziebart or some kind of undercoating.
In this pic you can see what I'm calling the outer frame covering metal. It is all the 'shiny' metal because I took the wire wheel to it. I wouldn't really call this steel 'plate' as it is pretty thin material. If I was to cut out and grind away this covering metal the thicker steel c-chanel is not rotten at all. On the inside of the frame you can see where the two pieces of c-channel come together, all solid steel. All the 'holes' are the thin outer frame covering that have rusted away. While I'm sure it adds a lot of rigidity it does not appear to compose the major structure or sub-frame. It is not obvious in this pic, but the hole above the bolt head you can see, where the trailing arm mount attaches, is where another piece of heavy c-channel ends and the outer steel skin rusted away. Again, the c-channel is solid and it is just the thinner outer skin that has rusted away.
The inside of the 'inside' wall of the frame looks to be solid and in great shape. It is the same on the outside of this 'inside' frame as well, solid. AMC used steel tubing (like DOM tube) that was welded into the frame for the bolts that pass through the frame. I imagine this was done so the subframe would not be crushed and so the holes would not cause a weak point in the frame. Two of these tubes look pretty rusty and would need to be replaced. You can see one of the two in this pic. This is another bolt that secures the trailing arm mount.
Here's a third pic of post-wire wheel clean up.
My dry erase skills leave something to be desired, but this is what I am proposing is how AMC built the subframe before covering it with what I'm calling the outer skin. The outer skin, best I can tell, is what gives the subframe its appearance of one continuous piece of steel.
So, am I way off base on how AMC built these subframes? The more I dig into this Eagle, the more I want to believe the outer skin can be cut away and replaced with new metal. Starting to think this really would be a fairly easy job for a skilled welder/fabricator.