Hoover Wind Tunnel 7500 Brush not Turning

Question

Hoover Wind Tunnel 7500 Brush not Turning. I have replaced the Brush

and the belt. The problem does not seem to be either to me. I believe
might be a missing part. The place were the belt hooks on is a metal pole
which never seems to grip the belt well. In fact it seems loose most of the
time and slips on the brush, causing the belt to eventually burn up. Could
there be a missing plastic or rubber piece meant to hold the belt taught 
on the metal pole?