roll bind

Roll bind happens when we don't have enough degrees of freedom for the solid rear axle to roll.  In fact the factory mustang suspension would roll bind.  Each mustang pivot is a bolt through a bushing which does not allow twisting or lateral movement on the control arms.

Ford got around roll bind two ways that I can see:
1) Very large bushings which have relatively low stiffness to resist pivoting on any axis allowing for lateral flexing
2) Open section control arms which have low twisting stiffness.  In fact a friend of mine told me the other day that a while back people began replacing the "flimsy" control arms on mustangs with tubular ones, which resulted in ripping the mounts out of the body.

I have to make the upper control arms for my car and will make them tubular.  I suspected that using rod ends instead of bushings would prevent the roll bind issues.  My friend suspected that a triangulated 4 bar will still roll bind.  I made up a little model out of a broken kid toy and some welding wire:

I found that if I tried to translate the "axle" laterally on of the wires would slacken, indicating that the control arms would resist this motion.  They allowed bump, and they seem to allow roll as long as I rotate the axle on its long axis a little to keep the wires tight.  Within the limits that I can tell with this crude test, I think I will be alright using rod ends and closed tubes.