Many people tell us that the big differences between the versions of the 4L60E are the cases and what engines the transmissions came behind, but OC Trans poo-poos that idea. They tell us that when you boil off all the other junk, the big change is right here—in the input shaft and drum assembly. The later model unit is seen on the left. The later model shaft has a larger input diameter and spline count, and it is slightly longer than the older parts. The associated pump with the later model input is also bigger and moves more fluid.