Bump Steer vs lack of positive caster vs death wobble....

So, I've been through all the threads regarding steering issues for all three makes of vans to see if I had missed any correct answers (or any worth investigating)....
It was my belief that lowering my straight axle 108 chevy would be no problem as long as I put plenty of positive caster in....Well, there is more to it than that!!

Briefly, caster is the vertical tilt of the steering axis (king pin) front2rear with positive caster being the rearward tilt of the kingpin at it's top...Positive caster assures that the van goes straight when you let go of the wheel and returns naturally to center after a turn....It is measured in degrees of rotation of the axle in relation to the pavement....If you add front rake to your van, that subtracts from positive caster..... IMO, all these vans should have a minimum of 5 degrees positive and it is adjusted by placing wedge shims between the axle and leaf springs........

So I personally made sure I have over 7 degrees of caster after lowering my van with an axle flip....
I went for a quick test drive across my (un) favorite bouncy bridge, and the van went left-right-left, trying to dump me out in the road....

I'd heard of bump steer but had never before personally experienced it, but my van has it bad AND IT'S TERRIFYING!
So I started to research just what the mechanical workings of this issue are and learning these things told me how to verify the scope of the issue...
On all these early vans, we have a "side steer" drag link setup, where the steering box is ahead of the axle with a pitman arm hanging vertically, pushing/pulling a drag-link front2rear that is connected to an arm fastened to the left kingpin/spindle assembly.... In factory configuration, the length and orientation of the drag link in relation to the suspension travel axis is situated so that the drag link does not grow and shrink in length as the suspension works because if you are holding the steering wheel when it starts bouncing the thing will jerk left and right in a bump-steer scenario....The dilemma is that the steering box is attached solid to the frame and the drag-link's other end is fastened to the axle that is moving up and down....

The way to know if you have bump steer is to bounce the vehicle and see if the wheel goes left-right as it bounces...
What I found was that I had changed the drag-link geometry during my axle flip in a way that probably can't be corrected....

The solution that I've come up with is to install a bell-crank and cross-steer tie bar that is level with the ground and 40-some inches long that crosses over and hooks to the passenger side steering arm.....

I just wanted to share these thoughts so that folks might properly identify their issue if/when these issues arise and consider that lowering (or raising) one of these straight axles can bring on unforseen issues....
Not sure how my story will turn out yet, but I will share either way...

A great book on this subject is How To Make Your Car Handle.
https://www.amazon.com/How-Make-Your-Car-Handle/dp/0912656468

I went to the "Havasu Deuces" car show this morning and I noticed that 99% of the strait axle cars were cross-steer rather that side-steer (also called cowl steer on street rods)...
Hopefully, cross-steer is going to solve my bump-steer...

I forgot death wobble....
It can be set into motion by a variety of factors including minor bump-steer, front wheel or tire not round, bent, or out of balance, loose king pins or spring bushings or any loose steering parts... A steering stabilizer shock will sometimes cover death wobble...

I went back and read all the threads I could find about steering instability, bump-steer, and caster issues....
What I see is that the knowledge base regarding these issues has advanced substantially in the last 12 years and that is a good thing!
Most of these issues come up continually and we now have most of the right answers, but we can work on finding solutions together when we can't find the right answer....if we all can be willing to share what succeeds AND what doesn't......

Wheel offset can cause instability or death wobble. While I have had dozens of vehicles with deep dish/offset rims and had no noticeable issues, my van was definitely an issue! Any bump, dip or slight change in the road and it would pull to one side. Even the breeze from a passing semi would send me all over the road. As I understand it, the wheels are constantly pulled back or outwards because of the extreme offset. The wheel with the most weight gets pulled more. As you can imagine, the weight balance constantly changes and counter steering just throws more weight on the side that is already loaded. Once corrected, it is now extreme in the opposite direction. Replaced every suspension component, added sway bars and stiffer springs, better shocks and went heavy on toe in and castor. All very minimal help! The correct offset totally eliminated that issue. This in no way implies that it handles like a modern vehicle, it is still a white-knuckle ride at 80 mph but the correct offset helped more than any other improvement I made! LT steer tires were also helpful but nothing compared to having correct offset.

I have officially eliminated my Bump Steer Issue!....
You are correct that rims with offset can cause handling issues!.....Most 7 inch wise rims are close to a 5050 offset while most 8s, 9s, and 10s have substantially less than 5050 back spacing.....

Other things to check for when mounting tires on your rims is to check for roundness and wobble when each rim is mounted on the balancing machine..... If you don't speak up and ask, the techs often mindlessly add weights until the machine okays it....This is a cost free (in time) check that is worth tipping to get...

Also, tires rarely live out their full tread life and often when you start getting a pull or a bounce, you will find a big lump in the tread where the tire is beginning to come apart...

I finished installing my cross-steer setup, and I could not be any happier with the results!!