Hey everyone, thanks for viewing my post. I'm new to the forum and I have a few questions about my 2004 ATP, specifically why my rear end failed. I received this bike from my father in law, and prior to him it had only had one owner. Both previous owners only used the bike for hauling wood and moose, not much else. Upon receiving my quad, I took it upon myself to service it front to back, changing all fluids, greasing all bearings and all that good stuff. When I was out on my second ride on the bike, I was going up a small hill on a fairly steep incline (30-40 degree) and the rear end totally failed. At the time I was not sure what happened but I heard a loud pop and started rolling backwards. I soon found that I only had front wheel drive and managed to limp it back home. On closer inspection I found that the rear driveshaft was jumping over the spines on the rear end and was not capable of any power output whatsoever. The input splines for the rear differential are totally bald but the driveshaft splines seem fine. Did Polaris really make the driveshaft splines with a harder metal than the rear end? Is this a common occurrence with Polaris ATV's? Or ATP's? And does anyone have any insight as to why this may have happened in the first place? As I said, the bike was used very minimally prior to myself owning it, but the use it received from previous owners was definitely more rigorous than what I am intending. This repair will cost me around $1000 (new input gears, driveshaft, seal kit, mounting bolts, oils, etc.) and I just want to make sure it wont happen again. Thank you in advance for any insight into this problem, anything and everything is appreciated! I will attach pictures of the splines as soon as I transfer them to my computer.