23 spline is plenty strong. Probably not for fulltime drags, but otherwise OK


I'm not familiar with Passion, but the Chrysler OEM OD unit is just that---a special 4 speed with an OD gear in place of THIRD gear. You swap the [Edited by Moparts - Keep it clean] lever upside down for 3/4 so that when you shift 1234, the transmission "reallys" shifts 1243. YOU CAN NOT modify a stock 4 speed. At the very least, the pinion, cluster, 3rd gear, and the mainshaft are all different. Easiest way would be to find a new one. I'm not a big fan of these---large gear spread and OD 4th means you are "really" running in 3rd gear for high.