S10 T5 does not always need an adapter plate. Adapter plate does three things. 1. It spaces the transmission case 5/8” further away from the crankshaft because the S10 factory shaft is 5/8” too long. 2. The 14 splines on the S10 T5 factory input shaft are not cut long enough along the length of the shaft to allow proper clutch disk movement (without an adapter plate). The clutch disk will therefore bind on the shaft and not move away from the flywheel far enough. An adapter plate functionally adds length to the spline travel and solves the binding problem. 3. The 1983—93 S10 T5 transmissions have a Muncie bolt pattern. The 1994—1995 S10 T5 transmissions have a Ford bolt pattern. Sometimes an adapter plate is necessary to allow you to bolt the transmission to your bell housing if there is a bolt pattern mismatch.
The Jeep shaft swap has 3 advantages. 1. The Jeep shaft is stronger than the factory 14 spline shaft. It has a 1.125” diameter instead of 1” diameter. 2. The Jeep shaft has 10 splines just like your Chevy transmission 10 spline shaft. So if you have a functional 10 spline clutch package and flywheel, you can keep that in place. That saves you the cost of a new clutch package. 3. The Jeep shaft has splines that are cut further along the shaft. This allows proper clutch disk movement. Therefore, you do not need an adapter plate if your transmission bolt pattern matches your bell housing bolt pattern. You simply need to trim the tip of the Jeep shaft to achieve the correct length.
There are 2 ways to keep the factory 14 spline shaft and not use an adapter plate. 1. Use a cut wheel to carefully lengthen the splines on the shaft. This takes a steady hand. You don’t want to cut too deep. I think I have a picture showing an example of this. This allows the clutch disk to properly travel along the shaft and move away from the flywheel. You still need to trim the pilot tip and buy a 14 spline clutch disc that will work with your current flywheel and pressure plate. Do NOT cut extra length in the splines if you use an adapter plate. 2. If you buy a 14 spline clutch disc, you can take a die grinder and grind away the rear corners of the splines inside the clutch disc hub. This will allow the clutch hub to travel a little further back on the shaft without needing to cut extra spline length to the S10 14 spline shaft. This allows the clutch disk to move the proper distance away from the flywheel. Do NOT do this if you use an adapter plate.
Lastly, your bell housing must have a 4 + 11/16” center bore to properly index the T5 input shaft bearing retainer. If there is a mismatch in size, you need to use an adapter ring. Often times the adapter plate already has a machined ring to compensate for different sizes. Check with the adapter plate vendor.
