An inter-axle differential assembly comprises an input shaft, an output shaft arranged coaxially with respect to each other, a differential gearing and a dedicated reversible lubrication pump disposed between the input and output shafts. The reversible gerotor type lubrication pump includes a rotor driven by the input shaft, and an impeller, both disposed within a pump body coupled to a side gear drivingly connected to the output shaft. Thus, the lubrication pump generates lubricant flow only during the differential action between the input shaft and the output shaft, i.e. when needed. An oil flow generated by the lubrication pump is supplied to various components of the inter-axle differential gearing through a gallery of fluid passages.