A method and system for monitoring and predicting failure in pumps on operating vehicles is disclosed. The method may comprise measuring a plurality of a pressure drops across an orifice in a case drain line of a vehicle operating in drive gear, determining an actual case drain flow rate for each measured pressure drop, selecting a plurality of the actual case drain flow rates, estimating for each selected actual case drain flow rate an estimated flow rate for the case drain line and displaying the difference between the actual case drain flow rate and the estimated flow rate for each selected actual case drain flow rate.