Death Wobble is likely on a Dana60 swap (or likely any solid front swap), and from what I've read, almost guaranteed on Super60. While I agree with the mantra of trying to solve the death wobble issue, rather than cover it up...this seems to be near impossible on a Super60.
After 3 weeks of tweaking on the steering and suspension, and test driving, the only fix we got to work was a dual stabilizer setup. I went with the Rough Country dual N3 kit and it seems to solve the problem. I still get a little shudder from time to time, but it never turns into death wobble, even at places where prior I could ALWAYS make it death wobble at specific speed ranges.
For extra piece of mind, we also used an old stabilizer shock that I had lying around and fabbed up a setup that resembles the stock set-up of 6.0 F250's (passenger side frame to track bar). It didn't seem to help with shudder, but it did SEEM like it made it sway less on both straights and turning. It could be all in my head, but even if it is, I feel it couldn't hurt things. I am running heim joints (large rod ends) on my radius arms (both where the lower arm attaches to my frame mounts, and my upper arms to my lower arms) AND on my pitman arm side of my drag link (read further as to why I have one there)
So if you are having death wobble issues, I highly
recommend running a dual stabilizer set-up. Even if you haven't yet experienced it, I'd still recommend running one anyways, just to be safe. No reason to not run the upper stabilizer also IMO.
Now for the second peice of advice...The frame up towards the front of E350's (at least on mine) is VERY
weak. It is MUCH thinner material than I, and any of my truck buddies, would have thought. Also the C channel set-up seems to be weakly done there as well...now this may be for crunch zone purposes and what not, but it is not good at all for any time of left-to-right/right-to-left strain.
During a test drive while we were making adjustments to figure out the death wobble situation, it got so bad it ripped the panhard bar bracket right out of the frame (we used a RuffStuff outer frame bracket)...the bracket was fine, the welding my friend did was all still fine, but it literally ripped a big jagged hole from the frame itself. I'll try to remember to hit up my buddy and have him send me the pic of the hole.
Our solution was to fill in the hole (cut the bracket off the ripped out piece, cleaned the piece up, and weld it back into place, then we reinforced that whole area by welding on a 1/4 steel plate (we used a plasma cutter to cut out holes around a few bolt heads, and a sledge and vice to make the two [around] 90° bends...I know, we are precision fabricators
). Lastly welded the bracket onto the now reenforced frame. It seems like it is strong enough now. I've put it through a few decent overland trips since and we can find no stress areas.
Oh and as to why we changed the pitman arm tie rod to a heim joint. The very first time I got death wobble in it, I completely lost steering (it's a miracle that it happened on an open road with plenty of room...just 20 feet before it happened, I was on narrow twisties)...the cause?...The tie rod snapped. That had to be a ton of force on it to snap it. Rather than spending money to get a new tie rod and pitman arm (the tie rod seemed to have opened up the hole a bit), we just filled the hole a bit with weld and redrilled it to the size of our misalign spacers, and used a spare heim we had on hand...If you run heim joint control arms (or use them for any part really) I strongly recommend to get a spare of each size/thread pattern that you use...also a spare set of spacers that you use with your heims.
After the first drive with the pitman heim, we felt that it would wear out the hole, so we fabbed up and welded on a C bracket to the pitman arm, to wrap the heim joint. Seemed to help.
1) Before attaching thing that could have a decent left-to-right/right-to-left force on the frame, check out the frame first and reenforced if needed! If you have already attacked such a piece to your frame, inspect it and consider reenforcing around it.
2) Carry extra parts that may take some abuse, especially if getting a new set could take awhile.
3) make sure to give a good torque check and inspection on important suspension and steering components of your rig.
4) If you are fighting death wobble on a solid axle, dual stabilizers (axle to the tie rod of each hub) may just be your fix...And I recommend running one even if you haven't got death Wobble before. Running a third stabilizer (passenger side frame to track bar) may not be a bad idea.
Feel free to harass me to post pictures of our work and/or of problems we ran into...I will likely forget otherwise.