Alright....I was abusing mine today, pushing it to the limit and it cost me.
I have some undergrowth around my pond that I was cutting with my 721D. I had the deck all the way up to the highest raised position and was cutting things like briars, small saplings and chopping up old rotten sticks. Well, I kept pushing too hard and started cutting saplings that were about 1 to 1.5" in diameter. Stupid.
Anyways, it was going fine but then suddenly the blades disengaged. I drove it up to the garage and inspected it. Here's what I know:
1. Both drive belts in the rear are still in their groove and tensioned.
2. No sticks or anything clogging the drive shaft running under the mower from the rear to the deck.
3. No sticks or anything in the universal joint/coupling on the drive shaft
4. No sticks or anything clogging any of the belts under the cover on top of the deck
5. No sticks or anything clogging the blades under the deck - I can turn them by hand without obstruction
6. When I pull the red button to engage the blades, nothing happens.....it doesn't sound like the engine is under any burden, it's just that nothing happens....