I.f.s.-i.r.s.

[Bruce R]

Traction bars

I remember reading somewhere that the traction bars that bolt under the leaf springs don't work, something about competing centers of rotation, the article said on leaf spring rears something called a birdcage must be used. You ever hear anything about that ?

 

[Old Iron]

What you are most likely referring to is where someone bolts ladder bars rigidly to the axle and the frame without using leaf spring sliders. That application does fight each other for center of rotation. There is a way to make that work but, not an optimum solution to the traction war.
Slapper bars work because they bolt rigidly to the underside if the axle but only float under the spring where it's mounted to the frame.
They have to be adjusted correctly. Their designed to minimize spring wrap and transfer the weight of the body to the rear tires.

Rear suspension has become very sophisticated over the years and require knowledge of how to get the most out of each style.
Caltacs built their version of a traction device and work extremely well.