In the laboratories of CTU in Prague, an inertia test stand was recently built for endurance tests of the internal shift mechanisms of passenger cars. With regard to the instrumentation of the stand, it can be used also for determination of lost power of the not-loaded transmission. In this paper we present the values for the no-load losses measured during different conditions (temperature, shifted speed, speed of rotation) on the automotive mechanical gearbox for the transversal disposition of the drivetrain.For the further usage of the measured values is important to determine the proportion of the different sources of losses. We are mainly interested to identify the proportion of the churning losses and losses in the sealing, since these two losses remain the same, whatever the load of the gearbox will be. The losses of bearings on input and secondary shaft were calculated with the tool available from SKF. The load of the bearings was calculated from the measured drag torque. The losses of the tapered roller bearings on the output shafts were measured. The viscosity changes nonlinearly with the temperature. To cover big span of temperatures, including the low temperatures, where the churning losses are very high, the gearbox was enclosed in an isolation box filled with coolant. To observe the gearbox temperature behavior in reality, the gearbox was monitored during different driving conditions.