As typical with ‘old’ equipment, service parts become harder to obtain every passing year. We were presented with a gearbox that had run satisfactorily for over 40 years, and in that time both the drawings and the expertise of the people who originally designed the gearbox, had been lost. When the call came in we were told that the end-user had the failed gear and that our client (the original manufacturer) only needed a drawing to tell them what to make such that they could manufacture and provide a replacement gear. However, when we open the shipping container with the original ‘gear’, what we found was no less than 30 pieces of what may have been a gear at one time. It was obvious that trying to figure out what the original gear design was would be at best a guess based on the extent of the damage. Given that one gear can not suffer the extent damage evidenced by this piece without similar and significant damage to its mate, we requested and received the other gear in the train. From that we could determine what the gear was before it was destroyed and thus could engineer the first gear we were tasked to develop. We also worked with our client to determine the duty cycle their customer was placing on the machine and found that there was a significant increase in the back-driving torque loads, and it was likely that these new loads were the root cause of the failure. With a reasonable picture of the original gear geometry, a fairly complete understanding of the failure mode, and finally an accurate assessment of the duty cycle and applied torque loads, we developed a completely new gear design that would still fit into the existing housing and machine frame and generated the appropriate drawings, specifications and material and heat treatment requirements. Once our work was complete, our client had both gears manufactured and placed back in service, and the system has been running fine for a number of years.