Before cutting the perches and hardware off Before cutting all the hardware off (So I know how it goes back on) Back on with vehicles weight on axle to measure stock castor (jack stands are for safety only, no weight on them right now) Measuring stock castor. Make sure angle finder is parallel to spring and spings are parallel to frame. Cutting off mounts. Make sure you mark where the old perches were located on the axle because your mounting the new perches 180 degrees on the other side. Makes it a lot easier.