I've read all of the posts so far. This story reminds me of an eye opening experience I had one summer back in the mid seventies while working at a local job shop. The foreman handed me a PTO drive shaft and said, "Make another one just like this one." So I did. Two days later, the customer brought it back. All but one of the caps were broken with multiple spider web cracks. What in the world could have caused this? The assistant foreman took the shaft and set it on a surface plate. He said, "Ya see where these cap ends don't lay flat. They have to lay flat at each end." In other words, the axes of the U joints have to run in parallel. If they don't, incredible twisting forces are generated because the U joints want to line up. The misalignment of the U joints can be created by twisting the drive shaft under high torque conditions. The telltale sign of a twisted driveshaft is a whole vehicle harmonic vibration that rattles the wax in your ears at speeds above 45 mph. By design, the driveshaft is the weak link in the drive train. After seeing what a failed driveshaft can do, if one plans to race, ever, have the driveshaft checked by a certified driveshaft specialist. No doubt, they will tell you you need a new one, and it will cost you more than your budget will dictate, but you will have the option of having the shop build you one that will handle the pressures generated in very high torque situations.
