Sky Render
Stig's Retarded Cousin
The problem is the AWFUL rear control arm design. The upper 2 arms are angled towards each other to provide lateral location of the axle assembly. This design inherently has binding in it, so Ford got around this by using squishy bushings.
By putting stiffer bushings in, you are eliminating the compliance that "allows" that bind. Instead, the torque boxes that the arms connect to on the chassis and/or axle will have to flex instead. The end result is that eventually those brackets will snap off.
By putting stiffer bushings in, you are eliminating the compliance that "allows" that bind. Instead, the torque boxes that the arms connect to on the chassis and/or axle will have to flex instead. The end result is that eventually those brackets will snap off.