WJ stearing upgrade

So i am not understanding why when this upgrade is being done that you have to use a 1/4 inch spacer to get everything lined up properly.
why is there that much a difference between the XJ and WJ.
Is it the bottom ball joint or is the WJ dana30 different.

ive done some looking in to it have'nt come up with the answer.I do know that there is a difference in the lower ball joint but can it can it be used in the XJ to correct this issue with the spacer.

From JKS's site...
The Flange Spacer is made from 0.25" thick steel to precisely position the XJ wheel bearing and hub assembly, ensuring proper alignment of U-joints and brake calipers. WJ components can be easily sourced directly from any Jeep® dealer or salvage yard.

I am working on getting all of the parts. I just dont understand why the problem exists.

the ball joints and u-joints on the shafts have to line up for when you turn.

From my understanding, the WJ front Dana 30 used different axle shafts (CV shafts IIRC) and has a different knuckle design. The spacers are allow the XJ unit bearings to line up with everything that is found on the XJ Dana 30.

Ball joint wise, you'll want to use WJ ball joints (the lower is WJ specific, the upper is shared between the WJ and the XJ Dana 30s).

*EDIT* No CV joints in the front axle shafts on the WJ as far as I can see. Likely due to differences in the unit bearings (as the WJ uses a different model unit bearing and different wheel bolt pattern than the XJ).

*EDIT #2* Some WJ's actually did have CV axle shafts on their Dana 30s (those with Vari-Lok).

Long story short: the WJ front axle is a Dana 30 but with substantial differences from that of the XJ. The spacers are needed to allow everything to line up when using the XJ unit bearings.