In Reply to: rear end posted by chris eby on December 23, 2018 at 12:34:51:
The trumpet-to-center housing gaskets affect the bearing adjustment of the two tapered roller bearings on each side of the spider gear housing. That adjustment can also be changed by using shims behind either the cups or the cones of the bearings.
You can change the ring-to-pinion tooth engagment pattern by moving shims from one side to the other to move the ring gear closer or further from the pinion. You could do the same thing by changing the gasket thickness between sides.
The pinion can be moved in and out with shims, too.
Since the parts catalog does not show shims in any of these positions, I assume that Ford felt that manufacturing tolerances were small enough to keep things in proper adjustment without using shims. After all these years and worn parts, it may be necessary to shim things to get them to fit properly. A mechanic with experience setting up rear ends can check the tooth engagement.