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DA917 Rolls without jacking check valves

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I recently retrofitted a hydraulic lift into my 917H, and since then things have not been quite the same since before the hydraulic installation. Unfortunately I exposed the hydro unit to pretty high pressures (>1000#) during relief valve shim calibration. In this over-pressure state I did observe hydraulic fluid leak past the check valve jacking/bypass stems. The charging and implement pressures have been within spec all summer, and the tractor has been working well mowing as well as working my custom front bucket I put on it. The key strange thing that it now does is that I can push/roll the tractor without jacking the check valves - before the hydraulic retrofit, I couldn't budge it without jacking the check valves. (I almost lost the tractor to rolling itself down a hill - the engine was off, hydro control valve in neutral. The parking break doesn't work.) The other thing it seems to do is hesitate to accelerate up hills - I can't get my skull around why a hydro unit (as a positive displacement pump/motor pair) would "slip", unless charging pressure was being lost. Is it possible my check valves are worn/leaking? Is replacing them a maintenance item? Is it possible my relief valves are leaking by prematurely (e.g. they aren't seating completely)? Is the hydro unit simply getting old, and internal tolerances have grown to allow internal leak-by? (Or is this all "normal" - I'm a newbie on tractors.) Thx! Ken

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I have three 900 - 7100 series with hydraulic lift they all do it if they sit a while. They don`t right after I shut it off though. D-17_Dave I believe explained the reason in the past. Maybe he will see this post. The pumps seem to drain back on the Sundstrand.

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