Panhard bar

"Panhard bars" can REALLY screw you up if not properly designed. This is because they can impose side to side thrust as the entire suspension and bar moves, and side stress on the bar and springs. As the axle moves upward and downward, the bar can do this, and it is just not that easy to design for suspension with lots of movement such as an off road rig with leaf suspension

What you likely need to investigate is called "Watts link" but even they can cause problelms.