The pinion is part of the output shaft, which has no pre-load. It's end play is controlled to zero by the angular contact bearing at the cover end (with selective shims)on p23 of the ZF manual. If the ring gear is installed,of course the pinion shaft will have drag from the pre-load on the ring gear. Hope this helps.
Here's part of an old post from Lloyd Butfoy on this board :
Lloyd Butfoy Posted April 28, 2003 09:07 PM
Mark the ring gear and preload it till you can only do one complete rotation while spinning with one hand
