I'll be installing an AA SYE kit on a 231J,
Looking at the spiral speedo teeth on the original shaft, vs the plastic drive gear that comes with AA SYE,, the plastic gear looks to be considerably larger diameter than the metal drive on the old shaft,,
How will that effect the mesh of the original speedo pickup ??

 

OK,
maybe answered my own question?
I asume the new SYE tail housing places the speedo sensor gear farther away from the stock location? making up for the larger drive gear ?

 

Generally the speedo gear is rotated depending on size of the gear. By using the same metal drive on the tail shaft, the gear is put in an off center pilot. Rotating it allows you to use many different size gears which have different tooth counts, but the same pitch. So when you install it you will have to make sure the gear teeth mesh with the worm drive, otherwise you will not have a speedometer

 

My apologies for barging in, how do you like the 231j t-case? How much work to install vs a NP231?

 

np231J The J=Jeep, so if you're XJ had a np231 already, then you already have a np231j. Often on forums for jeeps/Cherokees, the J is left off.