Hoover Windtunnel U6433-900?

Hoover Windtunnel U6433-900 When I opened up the bottom plate of the vacuum cleaner and noted that the flat belt was broken. But also a nut fell out – I think it goes to the motor pulley (The black spool that holds both bells). The rod moves back and forth is this right? I put the nut back on to the screw. But the rod does not seem to engage with the self propelled part. Did the rod brake?