I do not really know what cause it, as far what happened I just pulled it out from my garage to replace the shocks and just drove it back in the garage. I am really disappointed with this machine a lot of things I had to replaced fused blown out (overheating), collant leaking, oil line leaking, thermo switch, 12 volt fuse replaced, rear shocks replaced and now the differential case. All of this I had to do myself because the dealer that sold the machine closed down so I was not able to used the warranty. Then I found out that there was a CF Moto dealer in fairbanks through this forum and when I called them they said that my 1 yr warranty was finished last April 2017. This machine only has less than 500 miles. Is there a video online that I can use as a resource to replace the diff housing or maybe can somebody walk me through the process. I am new to fixing this kind of problem. I owned a 2003 yamaha and not even onceI had to replaced or fix something on that machine I still have it and still runs very good.