I'm not sure about the big rigs, but on a lot of the passenger car and pickup ball bearings, the inner race on the rear bearing is extended far enough for the seal to ride on the race, not the spindle. When doing a substitution with roller bearings, sometimes it's necessary to fabricate a spacer behind the roller bearing cup for the seal to ride on, and LocTite it to the spindle.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!