I have a custom 2000 E350 w/ an 06 F350 front end I have roughly a 6" lift and 35 x 12.5 Toyo M/Ts. The 4x4 conversion was done by Boulder Offroad Vans in Colorado. I thought I would share my experiences with death wobble since I have been through the ringer and some of you may benefit from my troubles.
Immediately after the 4x4 conversion, the vehicle drove great and had no steering issues at all. By the end of year 1, the stock steering gearbox was shot and had lots of slop in it. I tightened up the worm gear with the set screw and death wobble showed it's face to me for the very first time. It turns out having a lot of slop in the steering system can prevent death wobble, it's not until you ALMOST get rid of the slop that you have issues.
Next, I decided to swap the gearbox and that temporarily eliminated the death wobble. Soon after, the drag link was the next weakest link and the hole where the steering stabilizer shock mounts wallowed out into an oval and death wobble came back. I replaced the drag link and found more play in the attachment of the pitman arm to the gearbox, which was due to damaged splines and could not be tightened further. A new pitman arm and death wobble was gone.
After about 4 months, the death wobble was back and this time it was damaged splines on the pitman arm again. I did a bit of research and figured that my setup was causing too much stress at this location and I needed to reduce this as much as possible. I had a custom pitman nut made with a shaft on it so I could add a support bearing to take the load off of the steering gearbox output shaft.
This worked for a while until again, the splines on the pitman arm/gearbox output shaft were destroyed.
I did some more research and figured the best way to reduce the stress at this point was to add a hydraulic assisted steering ram. I bought a Red Neck Ram kit with a 1.5" diameter cylinder and fabbed up a custom bracket for the attachment to the tie rod and axle. I bought a new (refurbished) gearbox and sent it out to be drilled and tapped along with a new power steering pump to be modified for higher output flow.
At this point, I truly thought I was done. The steering felt great and the death wobble was gone! There was no slop anywhere in the system and life was good. Except for one thing...I had an alignment issue that was wearing the front right tire and causing the vehicle to constantly pull to the right. I looked around for an alignment shop that could handle this large of a vehicle and decided to go with 4Wheel Parts.
I left the vehicle there and about 4 hours later they told me that the alignment was perfect but that now it has a horrible death wobble if you hit a bump with the front right tire between 30 and 50 mph! The tech said that he was completely baffled since the steering system had absolutely no play in it and the tracking bar bushings and ball joints were in great condition. By the end of the day he told me that he was able to "tweak" the alignment and got it to drive without death wobble.
I was seriously skeptical of what he did so I drove it for a few weeks. Something was definitely not right, it still pulled to the right (slightly less) and although it did not go into a full epileptic seizure, it sure thought about it a few times. I did not trust the alignment so I brought it to High Country Performance to check it out. They said the castor was maxed out at 3.7 deg (good), the camber was 0 deg (good) but it was toed out 0.25" (not good). This was done to hide the death wobble. They checked the entire steering system and found no reason for this vehicle to have death wobble. Again, another shop was dumbfounded.
I had them set the toe back to 1/8" in and I mounted a GoPro on the front bumper looking at the steering system and took it for a drive. Knowing I could get it to death wobble by dipping the front right tire into a nice pot hole. This is what I found:
Looking at video #3, you can see that the axle is actually moving forwards and backwards as though the radius arms bushing are shot or not stiff enough. It seems that this axle movement is forcing a turning radius on the steering system, which has to respond by moving. This oscillates and hits a resonant frequency where it goes into a full blown death wobble. The tracking bar bushing looks good and doesn't budge. All other components that I can see are doing their job and don't have any play.
Now, I am having the shop install adjustable uppers to the ball joints so that I can stretch the camber all the way to 6 degrees, hoping that this will help the situation. If that doesn't take care of it, I will pull the radius arm bushings and see what kind of shape they are in. I need to see if there are harder bushings available or if these ones are just damaged.
Ultimately, I am very surprised to see this kind of axle movement and thought that there might be some other rigs out there that fixed the steering system and still struggle with death wobble. As I continue to play with this I will post here and give updates.
Wish me luck...