Do you have to drop the pulley off the shaft of the engine to change the belt on the transission. If so, is it left handed threads?

Hey Mark , it would be helpful for us to know the brand and model of your mower. Most diagrams we pull from archieves and model# is needed. You usually do not drop that pulley. There is a spring loaded tensioner pulley under your tractot that keeps the belt taught. Pulling back on the tensioner arm causes it to swing and release tension on the belt. Then in a rolling or peeling motion you roll the belt off either pulley. Every tractor I know of you mus also drop the deck and belts to the deck to replace this drive belt.