In my experience, which is limited, a leaf spring suspendended rear end lateral motion is limited to the the deflection of the sidewalls of the tires and the bushing in the leaf spring eyes. There will be a small deflection of the springs, however; Not knowing what you currently have installed, my simple suggestions are to upgraded spring eye bushings and lower profile tires. Hope this helps.....
Aluminum front spring eye bushings, slider shackles in the back with a pan-hard bar. Try to make the pan-hard bar as long as you can. This will give it a larger arc. About the only side to side movement will be in your tires.
Don't use a panhard bar with a leaf spring suspension. Leafs have a lot of travel, and a panhard will try to make the rear move from side to side. The end result will be a binding rear suspension, so number one, something WILL break, and number two, the binding will reduce travel, which is what makes a leaf suspension work.
Running a pan-hard bar with leafs can be done if done right. Making it as long as possible and running it level at ride height. At 4 ft long you are going to get less then 1/2" arc in 12" of travel. This would only be good in a road race type car that won't have much travel anyway. For a street or drag set-up I wouldn't use one.
By the way 392dart, how close are your tires to rubbing anyway?
I know what you mean Brent - I have a panhard bar on my Dart. But the bar WILL bind and limit suspension travel eventually. Frame rails aren't even 4' apart, so that makes it pretty tough to mount it properly and keep it that long. For a street car or drag car, it will break. Someone mentioned dirt track, where everything breaks from time to time, so I guess that would be acceptable to some. But you're taking a suspension system with a single plane of travel and introducing a perpendicular plane of travel that is FORCED if the springs move beyond say 4". Something will bind and break.
i am tring to keep the tires from rubing i have 275 on a early dart 66 and only have maybe 5/8 of a inch on both sides of the wheel well i did add new steel to my springs and had them rearched but remember (5 years ago ) when the car ran the rear end would rock all over the place around corner that was before i moved the springs i was just looking to keep the side to side motion out fo the car
I know want your saying Carter, but road race guys have been using them on leaf spring cars since the 60's. Anyway I came across this design today, it takes out the arc of the pan-hard bar and lets it move up and down with the rear end. It looks like it may be the ticket to me. what do you think?
I think if someone is looking for that much control, just drop the springs and go with a 3 bar system, or 4 link. Looks like alot to deal. To stop tire sway go with a bigger rim and smaller side wall tire.