A speed retarding device for a rotary nozzle includes a hollow cylindrical housing and a rotatable tubular shaft rotatably carried by the housing. The shaft has an enlarged drag sleeve portion carried in the housing and a shaft end extending through at least one end of the housing to receive a rotary nozzle thereon. A pair of support bearings support the drag sleeve portion of the shaft in the housing. An annular inner seal between each of the support bearings and the drag sleeve portion defines a cavity within the housing receiving a viscous fluid confined within the cavity. The support bearings are separated from the cavity confining the viscous fluid and an outer annular seal on the shaft adjacent each support bearing prevents environmental contamination such as water and debris from entry into the support bearings.