Sometimes that center "spacer" is actually a crush sleeve. It's too long initially, with a slight bulge in it, and the pinion nut is tightened a little at a time until the drag on the yoke is the correct torque in inch-pounds. Once that is done, then the backlash and tooth contact pattern gets adjusted. It's a "one and done" situation- - - -overtighten it, and you'll need a new sleeve to try again.
Jerry
