Briggs 5hp Quantum self propelled shaft not turning?

I have an old Yazoo 22 S22MB1 mower. Something popped while I was engaging the drive lever and the self propelled feature doesn't work. Should the horizontal wheel drive shaft coming out of the side of the engine be turning whenever the engine is running because it is not turning now? The spring attached to the cable that engages the clutch seems to be free also. Anyone have any idea of how that clutch unit is attached to the cable spring?