The P/G input shaft spline length has changed over the years by different manufacturers, and even today there is no set length or standard length in the industry. For example, below is a picture (Fig. 1) of (2) Powerglide 17-spline input shafts; the short set of splines are from a factory 1960’s untouched Powerglide, and the longer set of splines are from a current manufacturer. As you can see there is a significant difference in length.
This holds true today with the Turbo splines as well. Back in the mid-to-late 80’s, the Powerglide splines evolved into the Turbo spline/30 spline input shafts. When this transition took place a bushing had to be installed into the end of the stator support tube to support the input shaft, which also centered the turbine in the converter. When the bushing was installed, converter exhaust holes had to be machined in the input shaft on each side of the bushing surface area to allow the proper exhaust of fluid out of the converter (Fig. 2). Due to this design characteristic, the input shaft splines were kept short to allow for the exhaust holes and shoulder on the input shaft for the bushing in the stator tube to keep the input shaft and turbine centered. The shorter splines kept the input shaft from sliding through the turbine splines and preventing the shaft to sliding out of the planetary input gear. Over time, torque converter manufactures started installing a bushing in the converter to center the turbine and input shaft which allowed them to eliminate the holes in the input shaft and the raised bushing surface on the input shaft. With the elimination of the holes and bushing surface, the length of the splines were not limited, thus longer splines now allowed the shaft to float farther forward, which, in some circumstances, would allow the input shaft to pull out of the planetary input gear. The picture below illustrates what I am trying to explain (Fig. 3).
See how the shaft can pass through the splines farther?
Due to the many different spline lengths, we have changed our turbine spline heights to accommodate the various lengths. The pictures below show the difference:
Notice how the picture on the left has a pocket and the picture on the right has the raised set of splines? All of our torque converters now have the raised set of splines. Older units with the recessed splines can be updated as well. Welding a button in the bottom of the converter is a band aid and not recommended as that can create metal fragments from rubbing on the input shaft.
This evolution in Powerglide input shaft spline length that resulted in increasingly longer splines from a variety of manufacturers across the industry has resulted in a variety of torque converter manufacturers not only limited to Hughes Performance experience a problem with excess input shaft travel within the torque converter, resulting in spline disengagement within the planetary as noted earlier. Fortunately, only our GM95 and GM96 torque converters are affected by this evolution of input shaft design. Hughes Performance has made every effort possible to stay current with the industry, and update our torque converter turbine splines accordingly as input shafts have changed over the years. However, because Hughes Performance has so many GM95 and GM96 torque converters in circulation, there are many customers running older design torque converters with newer design input shafts, and that’s where the spline engagement issue can potentially become a problem in a Powerglide transmission.
If you encounter this problem with your combination, or would like to have your older GM95/GM96 torque converter updated, please send your converter to our facility ASAP. We will be happy to update your converter accordingly!
If you have any questions feel free to email myself at firstname.lastname@example.org or call me at 602-424-9892. Kevin Kleineweber Hughes Performance