Hi Jim. The later 140's as well as 120, 300, 312, 314, 316 Kohler and 317 still used a pinion and bull gear reduction arrangement, just in a different spot. For those tractors it had a pinion on the motor output shaft of the hydro that fed a bull gear on the shaft that led to a conventional ring and pinion type differential where the early style had the bull gear as the differential gear (since with the 90 degree orientation of the hydro motor there was no need for a conventional ring and pinion to turn the power 90 degrees to the axles). I don't know which design might be "stronger", but the later style hydro was probably a bit easier to "package" into the chassis and might have been a bit cheaper to buy. As a side note, the reduction gear/ring & pinion/rear axle housing on these later tractors was a Dana GT-20 assembly and was used in at least New Holland and maybe early Ariens garden tractors if not also in some other brands and is still available today (at least it is still shown on Dana's web site). I have never seen the early 140 style axle housing in any other brand (but that doesn't mean it wasn't used in other applications).