...When you look at the design features used to build a set of rear arms for these cars, conflicting requirements are immediately apparent. For example, in order to do a reasonable job of laterally locating the rear axle assembly, you need very rigid arms fitted with pivots that allow little or no deflection. If the pivots are soft rubber, they deflect and allow the axle to move about and degrade handling, so rock-hard bushings would seem to be the order of the day. But, that would be ignoring some of the other kinematics present in the system. When the axle moves vertically, you notice binding in the angled upper arms. This is because the upper arms frame side pivots are far off the centerline of the vehicle, but the axle side ends are very close together, causing them to swing in conflicting arcs. At any height except the car's original ride height, the arms begin to pull against each other and against the mounts of the axle. To reduce this binding, you need very compliant (soft) bushings to allow the arms to essentially change in length a fraction of an inch. If you don't do this, you have greatly reduced ride quality and some degree of undesirable suspension binding. Also, consider how, when the car's body rolls and the axle needs to articulate, that the arms need to be free to move in torsion. In other words, they need to be free to twist or, once again, you incur suspension binding and erratic handling issues. (From "How To Make Your Muscle Car Handle" by Mark Savitske)
Doug
