To ensure the specified reliability of hydraulic systems, it is necessary to search for technical solutions and develop a method for calculating its parameters that would have the necessary forecast accuracy to evaluate the developed hydraulic systems. To create a model of the reliability of a hydraulic system, it is necessary to develop a mathematical model of the process of managing the specified reliability of drives and their elements. The developed theoretical foundations for managing the reliability of hydraulic drives of self-propelled equipment made it possible to propose a methodological approach that allows forming models of drives and their elements under the conditions of their operation during the implementation of technological processes. The obtained mathematical dependencies allow determining the change in reliability indicators and functional characteristics of hydraulic systems and their elements. The developed models allow simulating the change in the technical condition of hydraulic systems and their elements under operating conditions of self-propelled equipment. Modeling the process of changing the technical condition of the hydraulic motor by managing its reliability shows that for the standard design of the hydraulic motor, the average value of the probability of the distribution of the control parameter values is 0.26, and for the modernized one - 0.04, with a limit value of 0.37. The average time between failures of the modernized the system rotors and the hydraulic motor as a whole is 6000 engine hours, which is 3 times higher than the average time between failures of the standard design of the hydraulic motor.