How can you tell if an 88-91 tranny is an Si? Is there a difference between 88 to 89 trannies and 90 to 91 trannies? Also, if there is no label on the tranny is there any way to know what tranny it is?

 

put tranny into reverse - position tranny with the input shaft and driver's side of the differential where the axle goes in facing you - using a white felt tip or paint pen, place a mark on the spline of the input shaft and on the spline inside the differential at the 12 o'clock position - rotate the input shaft counter clockwise exactly one complete turn - look at the mark inside the differential - if it is slightly before 9 o'clock position, it is Si - if it is slightly before 10 o'clock, it is DX - if it is slightly before 1 o'clock, it is HF and if it is slightly before 12 o'clock, it is Calif. HF.
88 has 21 spline input shaft - 89-91 has 20 spline input.

 

lol....

look at markings inside circle above the fill bold located on the passenger's side of the tranny if it says:

PL3
-------
3000

its an si

 

pl3
------
3000

Are the markings for a ZC tranny too...

but the Axle's are totally different..