The function of the automotive transmission is to reliably transmit torque and motion between engine and wheels at acceptable levels of noise, vibration and desired life.Gear drive components most commonly subject to distress are the gears, shafts, bearings and seals. The variables in the entire power-system, such as vibration, misalignment, type of lubricant used, material properties, operating temperature and abuse are considered as the main root causes for the gear failures. The bending and contact strength of the gear tooth are considered to be one of the main contributors for the failure of the gear in a gear set. Thus, Heartzian stress analysis has become popular as an area of research on gears to minimize or to reduce the failures of gears.In this research work, one of the major field issues related to 1st gear and reverse gear pitting at very low life for 6 speed manual transmission for mining/ quarry application is studied. The purpose of this paper is to identify the causes of gear failure, bearing failure, source of noise and suggestions for improvement on gear, bearing, and shaft life and to minimize noise in the system.For identifying causes of failure, complex dynamic model of gearbox including all details of gears, bearings, shafts and housing stiffness, etc. is built in simulation environment.Transmission error in gears is main source of noise from the gearbox, which is theoretically investigated from software simulation. Initial analysis in software environment is performed for correlating actual field problems, correlating pitting pattern between actual components and simulation results and for validating baseline mathematical model.One more important thing is to generate duty cycle for investigating gear box life. Actual duty cycle is generated for correlating actual and simulation field problems.For improving life of the components, macro geometries, micro geometries, materials, transmission error, etc. are studied and implemented both in software and real environment to improve gearbox life. Based on Duty Cycle, micro geometry modifications are suggested to improve the contact and bending life. Other design modifications are also suggested to improve gearbox life.The effectiveness of this model calibration technique was confirmed through comparison of unit dynamic characteristics in an excitation test and a calibrated simulation.