O. K. Unhook the coupler. Tape the coupler to the shaft. Do NOT push down on the clutch petal. Start the tractor and see if the shake is gone. If it is take the hydraulic unit off and pop the top shaft out of the transmission. Remember you will need to remove the long PTO shaft first. Also if the tractor has the gear case for a belt pulley it must also be removed first. Replace the bearings on both ends. More questions?