If you have a early clutch type Dana corp. posi unit in your 8 3/4 you may have a issue with the end play adjusters that slide into the cross shafts in the posi unit falling out when you removed the axles 1969 was a change over year on the posi units used in the 8 3/4 rear ends.
Take a flash light with a pencil type beam and look into the axle housing from the passenger side to see if you can see a hole in the cross shafts, if so that is the problem The end play adjusters slide into those holes and are use to put tension, adjust, the end play, on the other axle
You say it will(passenger side) adjust, screw into the holder, on the passenger side, is the adjuster screwed in all the way out of its holder?
If not adjust it in some more until it starts to get tight on the end play and then adjust for .003 to .010 max in and out movement on end play cold
Good luck, let us know what you find