When the teeth surfaces of a gear are subjected to excessive stress conditions, surface failure may occur. This can cause plastic deformation or removal of the contacting tooth surfaces, in some cases, surface fatigue cracks occur in plastically deformed regions under excessive contact stress, and these can also be caused by scuffing or wear failure. Most of the conventional failure criteria are stress based. As such, the stress analysis of a gear pinion is important for failure analysis. Further the residual stress present in a gear pinion arise during operation under higher loads and in many cases residual stress measurements of pinion can play an important role in prognosting service life of pinion. X-Ray diffraction residual stress analysis method can be used to measure residual stress of gear pinion in situations where failure results from overloading, stress corrosion, fatigue, stress concentration etc, hence stress analysis provides an abundant information in the characterization of gear wear failures. This paper also looks into the various wear particles produced under different load conditions as a result of varying stresses developed on the gear surface. Energy Dispersive Spectrum technique is also used for wear particle analysis of both morphological and compositional properties which are very much useful for the study of too small particles of the order of 5 microns or less. This work utilizes this method also for the study and analysis of wear debris particles . Tooth surface defects such as such as pitting, mild wear and scoring were observed. Residual stress measurement using XRD of pinion was undergone to characterize the changes after 12 million revolutions; a significant change is observed in XRD stress pattern, In addition spur gear geometry of FZG gearbox is modeled in ANSYS 8.0 to validate with experimental results.