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720 hydro question

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hey guys, new to the allis chalmers community..always wanted a 720, and found one with the ark 600 loader, 48 inch tiller, and mower deck.. the nice thing was the onan had been rebuilt 2 years ago, and less than 25 hrs.. i have been using it for a couple months, and no problems. was tilling with it today, and the hydro gradually quit.. no hydraulics, no fwd or back wards.. replaced filter, checked fluid, and all fine..was goin to pull the relief valve to see if broken spring.. thought i would check with u grues and get some opinions before pulling it out.. i would like to find a spare hydro as a apare..

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There is not bypass on these hydro's as you can shift the manual tranny into neutral to move without driving the hydro. Since it slowly quit, and you have replaced the filter already, make sure you don't have a leaky suction hose or bad connection from an old hard hose that could be sucking air into the charge pump. Also look at the input shaft from the belt and verify that the tranny shaft is turning when you put the pump on stroke. It could free wheel with no load and stall when you apply load. If this doesn't fix it your likely looking at pulling the pump, something let loose......

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