I went out and crawled up under mine while setting on level concrete, visually the pinion angle looks to be on the same plane or maybe a degree or two less than the transfer case output shaft just as Tom suggested. Mine has a 2.5" lift and the rear is probably closer to 3" of lift. (Ironman Springs)
Be sure on the IronRock arm you have the Heim joint screwed all the way in as far as it will go with the big lock nut on the
back side of the arm. See picture.
You can also cut some of the threaded length off the end of the Heim joint to allow it to screw all the way in to the bottom of the threads if you want. You will never need the additional length on the Liberty. I cut about 1 inch off mine before installing which allowed lowering the pinion angle to closely match the OEM angle.
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Supporting Vendor and Moderator of LOST05 Jeep Liberty CRD Limited
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