So I was reading through this section and saw a lot of misinformation posted and thought I would share what I know from rebuilding T5's for 18 years now. When I first started, I was rebuilding/building 3 to 4 T5's a week, now it's down to 1 a week or so as the demand for T5's has deminished.
First off, the V8 and 2.3L T5 share everything externally. The bearing retainer, cover, case, tailshaft housing and shifter all interchange. A steel bearing retainer from a fox V8 trans will fit a 2.3L trans(ask me how I know) and work easily, however, th 94 up will NOT fit, but can be modified to work.
Secondly, the input shafts for various T5's will NOT INTERCHANGE. I say this because I also saw that being tossed around, taking a 2.3L input and tossing into a V8 trans will not work. absolutely, positively will not work. Here's why, the internal gear ratios come from the various tooth counts of each gear inside the transmission. The very first gear ratio is the input gear contacting the larger front gear on the countershaft(solid gear at the bottom of the trans), these are designed as pairs, so an input shaft out of a 2.3L with a 4.0 first gear will not interchange with a 3.35 V8 first gear trans. I say first gear trans because that's how much transmissions are identified, by their first gear ratio. Various manufacturers used different first gear ratios, different input shaft spline and pilot bearing diameters, different output shaft lengths, different tailshaft housing designs, speedo placements, bearing retainer sizes and lengths, so grabbing a T5 for the sake of it being a T5 is a waste of time as the only guaranteed parts that will interchange are the 1/2 slider and the 3/4 slider and the 5th slider. Everything else is propriatary for that particular vehicle manufacturers version of the T5. So saying, swap the input out and it'll work, is an incorrect statement.
There were several versions of the 2.3L T5, with the largest difference being between the turbocoupe and the std n/a 2.3. The first gear ratios were different as well as the 2cd, 3rd ratios.
A 94 up V6 T5 is essentially the same as a 94 up V8 T5, with the exception of the gear metalurgical composition and some teeth count discrepencies. The V6 trans utilizes the inferior 89 and earlier gear set, made of a weaker steel, and has the same 3.35 first gear, but a different tooth count on 2cd and 3rd even tho the ratios are similar. A 2.3L input shaft will not fit into these transmissions and work. It might bolt in, but it will whine and make one hell of a noise as it dies once power is applied to it, if it will turn over at all. The other difference is the V8 and V6 trans both share the same input shaft, albeit different in metalurgical composition, but the teeth count and length are the same. The bearing retainer is also the same and interchangable between the two transmissions(V8 and V6), but are longer than any fox style bearing retainer. The 94 up bearing retainer can be used on a fox body(both 2.3L and V8), by cutting approximately .650" off the end of the tube. I use a steel band saw to cut it off or have used a cut off wheel to do it as well, then just use a grinder to get it flat and remove any sharp edges with a wire wheel. It's a nice upgrade to any 4cyl or V8 unit from 92.5 and earlier.
The case top, or shift cover as it's sometimes called, has changed over the years, but the one specific point I wanted to share was the sensor that uses a 7/8" wrench to remove it from the front of the cover. This was a neutral sensor that the factory was going to use for some purpose but never did anything with it. It can be unplugged or deleted by using a 91.5 and up shift cover. It will affect NOTHING on the vehicle. Everything will function as it did before deletion, and the computer will show it can't see the switch, but it will affect nothing as it uses the vss to determine whether the engine is driving or in neutral sitting still. I told a guy who installed remote starts that he could use that switch for manual trans mustangs to verify neutral for the failsafe on the remote start. He started using that back in the day with great results.
I had to chuckle when I read that 2.3L T5's were hard to find, when I have an entire rack of them, with desperate guys stuffing them into their V8 cars and then trying to pawn them off to me as a V8 core when they finally come to buy a good V8 trans for their car.
The good news is that most of the 2.3L trans I get in that have not been behind a V8, are easily rebuilt by replacing the blocker rings if the customer is smart enough to bring it in before it starts grinding into gear.
I hope this helps shed some light on the T5 tech. If anyone has any questions, feel free to PM or post up here, I'll try to keep up with it and answer them. I also want to toss out there that in 98 I went 10.66 on a T5 I built, running in true street for the FFW races, I went to 4 of them that year, but that was the fastest I went, most were 10.6X and 10.7X. That was with the 2.95 gearset.
A caveat has reared it's ugly head with my above statements. It's rare that I come across something about a T5 that I had overlooked, but someone recently brought it to my attention so I set out to figure out what was going on. It has to do with a V8 and 2.3L bearing retainer, the front 'snout' that the tob rides on and retains the input bearing and shaft assembly into the trans. The issue is that Ford(in it's infinite wisdom) decided to swap out the input shaft bearing for a larger diameter race and increased angle of the roller bearings on certain years of 2.3L transmissions. So, when you try to swap to a steel bearing retainer or a V8 one, the race of the input bearing is too large to fit into the recess in the retainer. Here is a pic illustrating what I'm talking about
You can see how thin the wall of the recess is on the 2.3L retainer(R) vs the V8 unit(L). Here is a pic of the V8 bearing race inside the 2.3L retainer:
And a pic illustrating the difference in the races:
Now, what's the solution? how do you put a V8 bearing retainer onto your 2.3L trans? Answer: remove the input and bearing assembly from the trans, press the input shaft bearing off, and install a V8 bearing and use that V8 race as the input shafts are the same size where the bearing presses onto it:
Use the V8 bearing and race in the V8 steel bearing retainer. Easy, no. Simple fix, yes. Bearings run less than 20 bucks even if you overpay. I get them for less than 10, just shop around. You must reshim the input after you replace the bearing, as there are shim(s) under the race in the bearing retainer. shim it so the input is fairly secure, but may have a few thousandths wiggle to it, but def not so tight that the trans is hard to spin. Sometimes the original shim is all that's needed, but I'm putting it out there that you need to ensure it's correct before installing the trans. Also remember to tip the trans(tailshaft up) as you remove the input shaft so the needle bearings will not fall down into the case and they will stay inside the input where they belong. D&D in MI sells a great manual for rebuilding the T5. They also sell every T5 V8 part you could want or need. Hope this helps.