Adjust your cable, it may be too tight, the adjustment is where it attaches to the tightener pulley arm. I think there is also a return spring adjustment, make sure it is pulling the arm back out of tension properly. Also double check that the strap-iron belt guide on the driven end is properly positioned. If that is not adjusted correctly or if a bolt came out it may not be "holding" the belt away from the drive pulley when disengaged. Good luck.