Primary function of a drive half shaft is to transfer torque from transaxle to the wheels in East West configuration powertrain vehicles. Conventional practice is to consider either 1st gear max torque or the Wheel slip torque, whichever being the maximum as design torque. However vehicle dynamics and Powertrain characteristics have a major influence on the Driveshaft torque and the torques experienced can thus go beyond the design torque. This questions the design endurance limit for the driveshaft based on conventional design. One such situation is the torque experienced by the driveshaft during vehicle coasting condition with gear downshift. The torque experienced in such a scenario can go beyond the maximum design torque leading to failure as was observed in Vehicle level validation test. The paper mainly discusses about modelling such a scenario theoretically by a system approach to the vehicle test phenomenon and evaluating the torque pre-emptively to redefine the design torque strategy. Variables required for the calculation were identified and their values were determined using the engine and vehicle characteristics. Furthermore driveshaft torque measurement was done on the test vehicle with strained gauge shaft and telemetry to study the effect of variables and to refine the model based on measurement data. Finally a co-relation between the calculated torque values and measured torque was done to understand the level of accuracy.. Modifications were also done to the part and bench test was done to understand the level of improvement.