Constant contact side bearing assembly for a railcar

A constant contact side bearing assembly for a railcar having a bolster with an upper surface and a walled receptacle upstanding from the upper surface of the bolster. An inner surface of the walled receptacle defines an open-top cavity wherein the side bearing assembly is accommodated. The constant contact side bearing assembly includes a spring and a base. The side bearing assembly base is configured to loosely fit within the walled receptacle and a gap is defined between an outer surface of the side bearing assembly base and the inner surface of the walled receptacle. A railcar engaging surface portion on a friction member is biased by the spring against an underside of the railcar. An adapter is configured to fit between the side bearing assembly base and the walled receptacle to, at least partially, fill the gap between the side bearing assembly base and the interior surface of the walled receptacle thereby positively positioning, both laterally and longitudinally, the side bearing assembly while reducing horizontal shifting movements side bearing assembly relative to the bolster to optimize performance of the side bearing assembly.