The pinion inner bearing on 11.5" rear axles (HDCS) has been changed for improved performance and bearing life. This new bearing will not fit with existing inner bearing cup installer GM-44417, but will fit existing Medium Duty Dana 80 axle bearing cup installer GM-45240. Due to the depth of the bore, approximately 10" from the cover surface, GM-45240 must be used with GM8592 Driver Handle to seat the bearing cup. To install, GM-45240 and the cup are placed into the bore, and driven to seat with GM-8592. Unapproved methods may not properly seat the cup.