in normal operation. Springs which have an arch to them will move the axle rearward when compressed and when you truss one it will cause lateral forces to be applied to the mounting points. that is why crossmembers are breaking. People are running rubber bushings or a shackle link to oppose these forces.
you have basically caused the springs to rotate using the housing and rear crossmember as leverages against the springs natural articulaion movements.
so your springs will take all the forces causing extra multiplied flex to the front half of the springs. (forced spring wrap) the springs cannot go forward and up at the same time with out bending to compensate for it. so either the housing mounts will fail or the rods attachment points or the springs which ever is the weakest.
