I recently upgraded a newer T-case with the 4.24 gear kit for my 1990 Geo Tracker. I knew that my original case couldn't be used so I kept searching until I found a mystery frame from a Suzuki Sidekick for $100 that still had everything on it minus the body and engine. I was able to identify that it was a 1991 or later so I grabbed the T-case for my build. I had previously searched for a newer T-case online and just about all of them were listed as 89-98 regardless of what year rig they came out of. I could easily see someone buying a T-case then discovering the hard way that they couldn't upgrade it. That made me wonder how to identify the difference between an 89-90 VS a 91-98 T-case. I searched the internet and found nothing on T-case identification in these years. A couple days ago I pulled my original T-case getting ready for the swap and decided that while I had both cases removed I would figure out how to visually tell the difference between the two. I found 3 easily identifiable differences between the two.

First: The flange around the 89-90 input shaft goes into the case about 1/2" deeper than the 91-98

Second: The big groove under the speedo flange goes all the way under the flange on the 89-90 while it stops about an inch short on the 91-98

Third: Right next to the output shaft there is a long flat area under the shift handle. On the 89-90 it is completly smooth. On the 91-98 is has a small hump right in the middle.

I made a Youtube video that shows the diffrence that you can view with this link: https://www.youtube.com/watch?v=76ToxWa60oY

I have a few other Trackick videos on my channel as well.

I may also need some clarification here though. From what I understand there is no difference between the manual transmission T-cases and the automatic transmission T-cases. A lot of sellers advertise that there is a difference and often sell the MT cases at a premium. Also I have heard that around 96-97 the output shaft splines may have changed. Is this true and is it a simple swap of newer drivelines to put one of these into an older Trackick?

Right, there are no differences between a manual tcase and an auto tcase. All 89-98 trackick tcases (no matter if they came from a 2 door or 4 door) will interchange.
In 96 the tcase rear output shaft changed to 16 spline (was 26 spline in the 89-95 ones). The front output shaft remained the same 26 spline as the 89-95 ones.
So to use a 96-98 tcase in an 89-95 trackick (or vice versa) all you have to do it swap the rear slip yoke on the rear driveshaft to the one with the correct spline.
One other difference you will find in trackick tcases is the shifter. The ones that came in 4 door trackicks with an automatic transmission (they have the 4 speed auto) will have a shifter with a different bend in it, because the 4 speed auto is longer than the 3 speed auto and 5 speed manual. So to line up in the shifter hold in the tranny tunnel the shifter has a different bend to it.
Any of course depending on the axle ratio, the speedometer gears in the tcase will vary.
Oh, and some of the early tcases had a "4wd-L" (4wd low) switch on the tcase that lit up a light on the dash when in 4wd low.

The difference in rear output spline counts is good info to have!  I bought a 97 parts rig for the transmission to go in my 95, and am trying to decide if I just want to keep the assembly together and swap it all in, or use my original case.  I guess if I don't use the later case, I need to keep the driveshaft to have the correct slip yoke.  Any idea on spline count on the later gen 2 cases?

The difference in rear output spline counts is good info to have!  I bought a 97 parts rig for the transmission to go in my 95, and am trying to decide if I just want to keep the assembly together and swap it all in, or use my original case.  I guess if I don't use the later case, I need to keep the driveshaft to have the correct slip yoke.  Any idea on spline count on the later gen 2 cases?

I believe the gen 2 spline counts are the same as the 96-98 tcases...rear output is 16 spline, front output is 26 spline.

So if I was going to do something crazy like put an XL7 rear end in my Sidekick, it might be better to use the later model case so I could have the XL7 driveshaft shortened and use it?  More scratching of the beard to come on this subject matter...

Now you got me scratching my head - why would you want to put an XL-7 rear end under a Sidekick?  It's wider, mounts differently, has no traction aids available to fit.  Yes, you might have it lying around, but, if you're going to go to the trouble of a custom rear suspension to fit it, just get a Toyota axle that can take a locker.

The long term plan is to 4 link the rear.  I also plan to run the 16" XL7 wheels next time I buy tires.  What is crazy is the XL7 track width with original wheels is actually narrower than my Kick is right now with its wild offset wheels.  Also, the lower link mounts on the XL7 rear will actually bolt right up into the Kick.  So it will be a fairly easy swap, and it will give me the track width I want with a small spacer.  I also have a weird thing about brand purity...no Yota parts here!

So if I was going to do something crazy like put an XL7 rear end in my Sidekick, it might be better to use the later model case so I could have the XL7 driveshaft shortened and use it?  More scratching of the beard to come on this subject matter...

I am not sure if the pinion flange bolt pattern is the same on the XL7 compared to the early trackick. If it is, then you should be able to just use the trackick driveshaft and just swap the slip yoke (that is assuming the XL7 and trackicks use the same ujoints). Of course all of that assumes the driveshaft length doesn't need to be changed because of XL7 axle placement, etc.

From what I have researched/observed by visual comparison...the XL7 pinion flange is different, and they XL7 rear driveshaft uses a bigger u-joint.  The XL7 front shaft uses the same u-joint as the Trackick, which uses the same joint from front to back.  I guess I need to go pull the rear drive shaft out of the XL7 and just make confirmation that it will work with the later Kick output shaft.  If so, when that time comes, I can just have a driveline shop shorten it to fit in my rig.