There are no grease journals in a sealed (non-greasable) trunnion. The bores are blind, and are not as deep as the needle races, so the shear load across each post is applied to a greater cross-sectional area than in a trunnion drilled all the way through (greasable).

Also, the 5th bore for the grease fitting creates another weak spot in the trunnion body. And the fitting's pipe threads seal by the wedging action (they're tapered) which also helps split/crack the trunnion of a greasable U-joint. Sealed joints don't have any of that.

Note the use of new grease in each cup; both to hold the needle bearings in-place, and also to fill/refill them before assembly.

See also:

Owner caption October 2016 · Photo 0 of 5000