While waking up under the front of the truck, the last thing remembered the night before being how good the single malt was (not really, I was just changing the coolant, but it makes for a better story :^), I had a few minutes to ponder the suspension. The track bar was interesting as it seemed to be the only thing that preventd side to side movement of the axle. It was also interesting as it was pivoted, so movement up and down would also cause a bit of side to side movement. Running some numbers it seems that hitting a bump where the axle moved up 2 inches and then down 2 inches from the stationary position would cause a bit over 3/8in of side to side movement. Down 2 inches and up 4 inches (I don't know what the actual travel is) could cause about 1/2in of sie to side movement.

3/8in to 1/2in isn't much, but it's significant as the axle is heavy. The only apparent damping of that movement are the shocks and maybe the tires in some cases, but in other cases the tires could make it worse. From looking at the setup it seems that if the axle were moving side to side it would also be causing the axle to move up and down, and since the axle is a lot heavier than the bars connected to the steering box it could also the steering to move back and forth, where the steering damper would the only thing preventing that.

Critical damping would be damping from the shocks, damping from the stering damper, and any help from the tires. That's why load range is important, as it relates to sidewall deflection uner load. Tire inflation is also important. Wjat might also be needed in cases would be an additional damper from the track bar to the frame, where it's connected to the axle.

Of course none of this may make any sense as I get over the hangover :^)

 

You'll notice that the angle of the drag link from the steering box to the tie rod is exactly the same as the angle of the track bar. So, as the suspension compresses and rebounds, the arc that the track bar follows is the same as the arc of the drag link. This causes the lateral movement of the axle to be countered by the lateral movement of the steering linkage, and theoretically, you will keep going in your intended direction of travel.

 

It appears that the axle has lateral movement as it moves up and down, due to the pivoting of the track bar. The drag link is connected to the hubs forward of the axle, as you need a moment arm for the steering to be able to turn the wheels. The drag link is also connected to the steering box, which is fixed to the frame. Driving straight ahead and hitting a bump the axle will still have lateral movement, and as you noted if the drag link is (about the) same length as the track bar and the same angle it will pivot in the manner, minimizing impact to the steering. It will be more noticable in a turn as the pivot points will be different.

It still doesn't minimize the lateral movement of the axle, which in addition to the up and down load of the axle and tires is another load that the shocks have to try to dampen. Big, heavy floppy tires can make things worse as they increase the load that the shock have to try tp dampen, and lifted trucks will make things worse as the angle that the track bar moves thru will be greater, resulting in more side to side movement of the axle.

Just thinking things thru, as opposed to having experience with these suspensions.