Craftsman Riding Mower Model # 917.272264 its about 4 years old. Cutting yesterday started hearing a grinding sound, but cut almost 2 yards before mower finally just when i press the forward pedal it wont go, but if i press the rear pedal it will go backwards just fine. Ive tried purging but still nothing we took back wheels off an keys seemed to be alined. Im stumped now can anyone help me? Thanks.