This paper tries to consider and analyze the effect of a torque converter influence over the coasting mode of a heavy military vehicle, considering the slip between the converter’s impeller-turbine blades. Since this interaction is an important source of drag within the transmission, when analyzing the dynamics of the coasting process it should be seriously taken into account. Testing an existent torque converter unit on a test bench is the best way to assess its internal drag, if the data provided by the manufacturer weren’t available. This paper aims at providing a procedure to reveal the transmission overall drag assuming the torque converter as being its main provider. The procedure roots over plenty of experimental research. Nevertheless, the induced friction within the transmission’s components has to be referred as an unloaded one. The tests determine the inertial moments of the driveline parts using the “falling weight” principle. Two approaches are available when comes about assessing the torque converter’s hydraulic inner drag, i.e. the laminar flow approach and the turbulent one. As the laminar approach was the topic of a previous evaluation, this paper goes for a mathematical model if turbulent flow was considered.