This thesis looks at how vehicle gears are designed, manufactured, maintained, and improved to ensure reliable performance. Since gears sit at the heart of any transmission, getting their design right has a huge impact on how well a vehicle handles power and how long the system lasts. The work begins by comparing how automatic and manual gearboxes age and what each one needs in terms of preventive maintenance. It then moves on to the design of a helical gear, created using CAD tools. After that, the study builds a detailed model of the gear-manufacturing process with plant simulation software to show how production would run in practice. The final part reviews the results of that simulation to see where the process can be tightened or optimized. Taken together, the study connects design, maintenance, and manufacturing so that the complete gear-production workflow can be better understood and improved.