I was mowing and everything was going well for over an hour. After finishing one section, I moved to a new area of the yard and engaged the PTO... while the deck was in transport mode. It ran like this for about 5 second. It was after the 5 seconds I noticed the wild vibrating and that the deck was in transport mode. I lowered the deck and restarted the PTO. Same vibrating. What happened? How to fix?
Blades are not bent
Bearings are all solid
Both belts are fine (drive belt OK), (deck belt brand new)
Idler spring set to proper tension when in cutting mode
Seems strange to me that this would just start suddenly, as it did.
One thing is for sure hempdiddy. There is a lot of vibration going on under the deck from something. Looks like your going to have to take the deck off and recheck your rebuild. Please keep us posted on what you find.
Should you find no issues with everything that has been mentioned you may have stretched the drive belt.
I understand that you mentioned it was visually "ok" but belts can and do stretch over time. In my experience a tensioner moving that much is not at the right tension (adjustment, worn, etc) or the belt has stretched.
I also read through my operators manual for the J series deck and found no specific warning for engaging the PTO in transport mode, however this seems to be the event that triggered your current problem. Suspect this is an old belt and the angle of the belt in transport mode coupled the initial torque of the PTO engagement caused the belt to stretch.
If you do arrive at the conclusion of everything else being okay, I'd get a new drive belt and compare them side by side for confirmation.