Thanks for the reply, but I haven't filled the system. I just assumed draining it would result in air trapped in a few places. I just wanted to be sure I did things right if there was a specific procedure to follow when refilling and operating the tractor again. My assumption is to fill the case until the dipstick shows full, then operate the tractor and hydraulics briefly, recheck level and fill if necessary, repeat if necessary.Did you check sump screen for clogging? There should be no air in hyd system just air in trans case(sump). Check hyd oil with engine idling nut on dipstick resting on threads,fill to full mark on stick.