D30 axle shaft differences between 1998 and 1999?

I am trying to identify a noise coming from the front end of my '99 XJ and want to swap in some complete axle shafts that I have from a '98 dana 30 to see if the unit bearings are worn.

My question: is there any differences between the size of the u-joints? I am assuming that there isn't a difference between anything else. I have been holding onto these axle shafts on trail runs in case of breakage. Let me know. Thanks.

No difference. Other than a year older that is... Any non-disco D30 shafts with the correct factory splines will fit your factory D30.

What year did the u-joint size change?

Shafts are the same, unit bearing design changed halfway through 99. Check the height of the hub ring in the middle (right around the axle shaft nut) - if they are the same height, you can use them, if one is taller, you can't.

That's exactly the info I was looking for. Thank you.