I just experienced DW for the first time this weekend...WOW! I just have 35's on 4" springs and ORD's HD shackles (front springs). The tires ARE balanced and like new. I never had an issue with my 10B on the same suspension. I have brand new ORD X-over and tie rod setup (thus no steering damper). I experienced it when I hit a small bump, hit the brakes hard (I was bedding in new pads), even for no particular reason it seemed. I tried accelerating thru it, but that did not help. Had to stop on a 50 mph 3 lane road! That sucked!
So...I have been thinking about the issue. It seems like once it starts, it resonates the whole front of the vehicle. I figure there are several things going on, and I don't think it has to do with the tires (in my case). Once it starts, it doesn't stop until the vehicle is ~3 mph. First, I will be replacing the cones and springs. Next, I will try to put a single steering damper on there. I will also check the U-bolt torque. I have a feeling though that it is more than these things as the root cause. First, the axle is much heavier than the 10B it replaced. Are the shocks sufficiently damped to control the added mass? Probably not! Second, the reason we put the springs we do on our vehicles is for wheel clearance and flex. Well, the wheel clearance doesn't help any from a load standpoint. Basically, any side load on the axle goes through the springs and shackles to the frame. The moment arm is longer now with the lift springs/longer shackles, thus less stiff. Additionally, the springs are intended to ride softer. I think that the axle needs to be controlled laterlly, al la the panhard bar (or whatever people call it on 4x4's). Think about the Super Duty...they run Pan Hard bars on the leaf spring trucks. This will limit the lateral motion of the axle, so now the springs don't need to control this through twisting. A x-over can act like a panhard if you have the hydro-steering on there, thus the reason the hydro works as a band-aide.
I have reas stories on here where guys have completely rebuilt their axles, yet still have DW. Then they tighten the U-bolts, and it goes away for a while. I think that the U-bolts are helping to stiffen the springs torsionally, thus allowing them to twist less...helping the DW.
So, why don't stock trucks exhibit the DW? Well, the springs are reverse arched in most cases, so they have less moment arm, and are also probably naturally stiffer. They also are in a more stable orientation (reverese arched). This about balancing a hammer vertically on your hand. It is unstable (similar to the lifted truck). Now hang it between your fingers, it is stable (more like a stock truck).
Imbalanced tires will always be a problem, especially with large tires.
I think the root cause though is deeper. Alignment is probably also a reason (toe in alignment that is). Obviously worn parts is also problematic.
So, the real solution (if my theory is correct) is to add a panhard to the leaf sprung trucks...or 4-link and coilovers (or similar). Personally, I would rather go coil-overs...but that isn't going to happen any time soon. I guess I will try to put a panhard in and see what happens. Anyone have any examples of this? How does my theory sound?
Joshua
