We've got a small fleet of Toro Groundmaster 300 series mowers. This winter, we rebuilt the spindles in several of the decks. Last week, I was on vacation and one of my guys had a spindle fall out of his mower deck while mowing. Just fell out. He heard a rattle, and found the spindle and blade lying in the grass. This is one of the decks I rebuilt myself. I'm not immune to making a mistake but I really don't think I forgot to tighten the nut. And...if I did, These things are designed so that the nut tightens with use instead of loostening. The spindle looks good except for some obvious nicks from coming apart at 100mph. The top bearing and nut are missing but the pulley is in good condition. I've got a new assy. on its way to me via next day air but was just wondering if anyone's seen this before and if there are any good guesses what would cause this.