Been doing some research on what may be causing the jerking of my QT 16. Didn't make any headway towards solving the problem but did eliminate a couple things. It only jerks when under a load going forward. I backed it up my drive as hard as it would go for about 40 yds. Smooth as silk. Tried the same thing going forward and got the jerking action that kept getting worse if the speed is not varied. If I slow or increase the speed it is smooth while making the transition, then the jerking starts again. Drive shaft is not slipping on the input shaft. Brakes are not dragging. With the rear wheel jacked up I can turn both forward till the slack is out, then backwards and the tires only turn about 1+ inches so the bull gear, etc. is good. Both hubs are solid to the axles so not a sheered key situation. Also with the rear jacked up, fast idle and a 2 X 4 against each rear wheel I cannot duplicate the jerking. The down grade hold back is good at all speeds. Would think if a tooth was gone on a gear it would show up with the 2 X 4 treatment. Fluid and filter have been changed and the hydro is right on the full mark with engine off. Filter is not leaking but did find a very minor leak on the return line. Suction line was solid and not leaking. Filter is tight, no leaks. This is the Sundstrand hydro unit as it has the free wheeling valve. Eaton don't have that feature.
Any suggestions that may be the cause are welcome and appreciated. I really like this tractor and 50" deck but can't use it with the jerking all the time. Don't work to mow backwards either.