Dumb question:I have the TC off my transmission and am looking at the splined shafts. There is an outer one and a smaller one inside the outer one. Which one is referred to as the input shaft? On my trans the spline count is different between the 2 shafts. I know you have to match up the tc pilot or hub to the crank register and the correct spline count to the tc and trans. I just don't know which of the 2 shafts is the input. I suspect the inner small one but need to know for sure. Thanks.

correct & there are no dumb questions.

Thanks and I hear you. What is the larger shaft called?

I ain't for sure but it might be called the reaction shaft

The inner shaft is the input. 3 different shafts. Standard 67 and up non lock up, 24 spline normal for available converters, 66 and earlier 19 spline, and lock up 23 spline. The outer splined portion is the stator support. 66 and earlier stator support inner diameter is smaller and will not accommodate a later 23/24 spline shaft. The earlier shafts and lock up shafts can be swapped to fit the 24 spline shaft if the proper reaction shaft support and matching high gear drum are used.
Doug

DVW good info (going in my notes)