if the bars are parallel to each other, meaning if the 2 bars on each side are in line with each other going in the same direction, and if you were to look at the suspension from a birds eye view with the bed removed, (you will have to visualize that in your head) and the bars from the axle to frame are parallel to each other, that is your problem.

the sway bar is NOT the same as a track bar and will allow the rear end to shift from left to right. there should be a trac-bar setup just like the front ends have to limit left to right axle movement.

I think you are stating that this is the basic design of your bar setup in relation to mounting points, disreguard the blue leaf spring


you MUST triangulate the link bars in a similar fashion as below or use a panhard bar / trac-bar / watts link to maintain axle left to right stabilization.



this is more than likely why you had problems keeping the truck on the road. the rear end does not have to move much left to right to make a HUGE difference in the way the vehicle tracks going down the road. you want ZERO left to right movement of the axles.

 

Hi-

I agree, the first pic looks like exactly like what I have. However, if you are looking at it from a birds eye view, I have a bar going across behind the rear axle that rigidly connects each end. Then there are 2 linkages that connect that bar up to the frame. So that bar is solid and keeps the axle from moving from side to side. From first glance you would assume it is a sway bar, but in reality it is stabilizing the axle. I will get a picture of it as soon as I can get under the truck.
I understand that having a moving rear axle feels a lot like having 2 flat tires in the back... this is not the case for me. When I am on the highway it tracks true, and has not issues. It corners fine too.

 

the bar you are referring to is a sway bar. I saw pictures of it in your photo bucket album. it is not designed to restrict left to right axle movement.

I agree it is the only thing at the moment that is keeping the axle under the truck, BUT it is not designed to restrict left to right movement, it is designed to transfer torsional forces when one side of the truck suspension is loaded, it applies an equal or near equal force to the other side of the suspension to keep it loaded, and therefor reduces body roll and keeps the truck from "swaying".

Once you install a functional trac-bar, panhard bar, or a watts link setup, or you install a triangulated setup with your link bars, your rear end death wobble will still be there.

You can add 2 bars like the center ones in the second picture above. this will make it a 6 link suspension and will limit the left to right axle travel elevinteen times as much as the anti-sway bar that you have installed currently.

FWIW, I had an Expedition that had a factory 4 link rear suspension on air bags. they were a parallel 4 link with a panhard bar. it also had the EXACT same style anti-sway bar as you currently have installed. if Ford had thought that the anti-sway bar with end links was sufficient enough to restrict left to right axle movement then why did they install a panhard bar?

 

Thanks for that info... I am going to take a really good look and see what I have, but I will look into making up some sort of axle locator. I dont think I am noticing ill effects currently though. However, do you think this has anything to do with my vibration under load?
I have heard that the 2 bar system is prone to twisting of the axle resulting in varying angle on the drive line, so I dont know if this is the problem.
Like I said, it drives much better with the air sacks inflated... which I guess would tilt the diff up slightly, as you can see in the picture that I marked up.

 

these trucks exert so much torque, the rotational forces when multiplied through the drive line can cause weird things to happen, but having a structural sound rear suspension should eliminate vibration under acceleration

 

Alright well I think the first thing I will do is replace the u-joints in the DS... they looked good and felt good, but its the cheapest fix. Then apart from running the air bags up full, is there anything that can help to prevent axle rotation? The panhard bar will prevent the side to side, but not rotation... Even still, the DS angles dont seem excessive at all... so there has got to be something else going on.

 

just make sure that the U bolts are tight. looking at the top bar they look stout enough to eliminate rotation, but crazier things have happened....

 

Hey,

Thanks for all the input. I will update with any progress. Im making a parts run state side the weekend after Easter, so after that I am going to replace the DS u-joints to eliminate that chance. I also have a leaking TC seal likely a result of the vibes. I will check over all u-bolts and connections to make sure they are tight. For the long term I will look into an axle stabilizing device of some sort.

Thanks again… fingers crossed this helps!

 

for reference of anyone viewing this thread,

this is a Watts Link



this is a panhard bar



and this is a panhard bar and an anti-sway bar with end links attaching it to the frame.