Just bought a 08 x520 with 295 hrs from local JD dealer. Cut the front yard 1/2ac just a trim.ran great cut great. Went to mow the side lot and lots of vibration stopped tried again,same, saw part on deck, lowered deck all the way and clutch /pulley falls down on front of deck. Taking to dealer, but what could have caused this? Didn't run over anything but grass, not sure if I engaged blades with deck locked in up position. Ever happen to anybody else.