Hi Jack,
this image shows how the friction drive engaged and disengaged but the other Victa drawing did not
have this detail.

It's a little dangerous if a blade comes loose,I read about a blade that snapped off and flew
25 feet from a neighbour's yard,shattered a glass window and severed an artery on a 38 year
old's neck,there were lots of reported deaths from mowers on Trove.