I just purchased a Gravely 810 riding mower / tractor. It runs and mows, but does have an issue. The pto will NOT disengage. To "fix" the issue, an aspiring previous owner jury rigged a manual "tension mechanism" to the mower deck. When released the tension on the belt "slips" and the blades do not turn. To engage the mower, one dismounts the seat, manually positions the "tension mechanism", and off you go. Not perfect by any standard, but workable.
That said, I'd really like to fix the problem. Looking at the parts diagram for the transmission I can not begin to see how the pto is designed to engage / disengage. Any help would be greatly appreciated.