Rotor_Man
Guest
Not sure if this applies to a 1680,but on a 1480 with a worn shaft_coupler you must check the pump alignment. That little "bellhousing" adapter that mounts the hydro pump to the pto has no dowl pins to align it with the shaft. It may be right on,or it can be as much as .020 or more off which will destroy a coupler_shaft in few hours. The procedure to align this housing is in the shop manual. You mount a dial indicator on the pto shaft,and allow the pointer to run in the pump hole in the adapter. You leave the adapter to pto bolts barely snug,and use a hammer to shift the housing around untill shaft to housing runout is only a few thousanths of an inch. The closer you get this,the longer the coupler_shaft will last. When you get it as close as possible,then lock down the bolts.