Yes you are missing the the big nut under that cap with a carter pin through the nut , all covered in grease i would imagin , the whole hub has to come off the rotor and hub are all one piece, the bearing and all come out , itf the truck has that many miles on it I think i would clean and check the bearing for pits or ware while i had it down and repack the bearings .
when you tighten that wheel and bearing back up tighten the nut till the wheel freezes up and back the nut of just enough to where the wheel turns easy , leaving the nut as tingt as possible with out the wheel draging when you spin it , the wheel should make a full turn or 2 when you spin it.


