The study considers the issues related to improving the system for diagnosing the technical condition of mining excavator transmissions and extending the service life of their working fluids based on assessment of magnitude and nature of changes in the acoustic signal D of the ultrasonic range in moving parts of transmission elements during its operation. The quantity and quality of the lubricant determines the value of the indicator D, and allows to make decisions about timely replacement or disposal of used transmission oil when implementing the technology of routine work within the framework of maintenance and repair strategy based on the actual conditions. Recommendations are given for improving the assessment of technical conditions of components and friction pairs of mechanical transmissions of equipment. The results of the experiment on changing the D index in a friction pair as a function of pressure in the contact and the angular velocity are presented. A block for cleaning transmission oil in mining excavator systems is proposed. A description of its operating principles is given.