The task of developing universal methods with high reliability of quality assessment, design, and diagnostics of the technical state of a tractor requires taking into account the design features and conditions of its operation. Determining the causes of tractor gearbox malfunction and subsequent repair is a complex, lengthy, and expensive procedure. Therefore, the development of a method for diagnosing a tractor gearbox malfunction without disassembly is a complex and demanded task. The quality assessment of gearboxes was carried out based on the analysis of the scatter of the maximum and minimum vibration levels of the sample of gearboxes. The assessment of the possibilities of reducing vibration levels due to compliance with the technology of production of gearboxes was carried out with minimum vibration levels of the sample of gearboxes. Analysis of the results of experimental studies showed a spread of maximum and minimum vibration levels from 10 dB to 25 dB. This testifies to the high instability of the technology for manufacturing parts and assembling gearboxes. As you know, the transition of the mechanism to another class of a technical condition is 8 dB, and an increase in the vibration level from 16 dB to 20 dB is the limiting value of vibration. Therefore, we can conclude that tractors of the T-150K type, already at the production stage, produce different classes of technical condition from 'good' to unacceptable for operation. Statistical processing of measurement results was carried out. The mean square deviations of the vibration of 17 gearboxes were determined for eight measurement points. The main reason for the accelerated malfunctions and decrease of the lifetime is the excess of the vibration in the gearboxes over the permitted level.