Military tanks and armored vehicles use tracks with excellent mobility in rough terrain, the transmission, a key component of tracked vehicle driving performance, performs shifting, steering and braking functions of tracked vehicles. There was concern about the deterioration of the driving performance of the tracked vehicle due to the occurrence of oil leakage in the output part of the transmission that rotates the track of the vehicle. Throughㅇ failure mechanism analysis and characteristic factor analysis using 4M(Man, Machine, Material, Method) quality management, it was confirmed that the factor affecting oil leakage in the output part was damage to the output shaft coupling surface, which is the contact surface of the output part oil seal. Based on this, a quality improvement plan was derived by applying a protective cap to prevent damage to the coupling surface, increasing the coupling surface hardness to improve the oil seal sealing function, and revising the work standard throughout production, process movement and assembly stages. The effectiveness of the proposed improvement was verified through a single transmission test, a power pack test, and a track vehicle installation test, and the effectiveness was verified through follow-up observation. It is expected that the improvements derived from this study will be utilized in the future analysis of similar equipment quality problems.