A constant contact side bearing assembly configured for insertion into a walled receptacle provided on an upper surface of a railcar bolster. The side bearing assembly includes a housing assembly including a base and cap receivable within the open top walled receptacle on the bolster. The base has laterally spaced sides and longitudinally spaced ends. The cap is guided for movements relative to the base and has a generally flat railcar body engaging portion along with structure which combines with the sides and ends on the base to define an internal void for the side bearing assembly. A longitudinally elongated and generally rectangularly-shaped elastomeric compression spring is arranged in the internal void within the side bearing assembly for absorbing, dissipating, and returning energy imparted to the side bearing assembly during a work cycle. During a side bearing assembly work cycle, the spring is configured to deform in a predetermined manner and such that, upon maximum spring deformation, the spring maintains an operable relationship relative to the housing assembly of the side bearing assembly.