as an u201c o u201d ring 21 is positioned between the outboard opening in the wheel hub 14 and the inner end of the heat dissipating end cap 20 to form a closure of the outer end of the lubricant receiving cavity or lubrication chamber 18 formed between the wheel hub 14 and the spindle 16 the heat dissipating end cap 20 is formed with an opening which extends from an outer surface thereof 22 into the interior of the lubrication chamber 18 so that oil may be introduced into the lubrication chamber 18 to fill the lubrication chamber 18 to a desired level a threaded closure such as a threaded plug 25 forms a removable closure through which oil may be changed or added to the lubrication chamber 18 unlike a grease filled lubrication chamber wherein you cannot pre load the lubrication chamber on bearing cavity 18 the use of the oil bath of the instant invention permits a pressure pre load of the bearing cavity or lubrication chamber 18 preferably between 5 10 ft lbs to facilitate the maintenance of a proper quantity of oil within the lubrication chamber 18 the outboard face of the heat dissipating end cap 20 carries a transparent window 26 sealed thereto through which the oil level may be conveniently.