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Discussion Starter #1
got a 1995 jd 8770, hydraulics failed and it was limped to the shop. hydraulic pump was replaced and also steering valve block, it was leaking, and now everything works but its loud. when you steer, raise or lower an implement its loud like the system is moaning and groaning. acts like its starved for oil but its not, lots of oil. we can olny get 20 gmp on the scvs, should be almost 40 mechanic thinks the brand new pump could be faulty, anyone else ever had such a problem?
 

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Did the old pump completely blow up and send fillings into the hyd system. Was the complete hyd system flushed after the pump was replaced. Also what rpm and pressure are you checking the flow at. John deere tractor you check the flow at 1000 engine rpm and 1500 psi on the flow meter.
 

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Discussion Starter #4
no the old pump didnt explode, no filings in the filters, but some bits of grit were found in the diff lock valve and the steering valve, could be something like that plugging somewhere. charge pump is good good pressure there. we think its either an internal leak somewhere or a valve stuck, causing the pump to constantly run or else a bad pump not sure where to start
 

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In order to see if the main pump is not destroking you need to put a gauge on the lube pressure port behind the lh fuel tank. I believe the 8870 has a electric destroke solnoid on the pump. Idle the tractor up until you get 10 psi lube pressure and then power up the destroke solnoid with power from the starter and see what the lube pressure does.
 

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Discussion Starter #6
i appreciate all the help on here, its great. well john deere mechanic was out at the farm for 3 days now we have eliminated everything, all thats left is to replace the charge pump itself. they will call me monday with a price, it looks easy enough to change and hopefully this fixes it. everything on the tractor is working but all tests show the charge pump only produces 18gpm instead of 38. i was told charge pumps do not often need replaced, that why they left it until last.
 

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Discussion Starter #8
i have checked the hose and the screen thats inside the hyd fluid reservoir and it all seems ok, how was it sucking air? and also how would i stop that?
 

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Discussion Starter #11
yeah,at least im not paying for them, but they tried a new charge pump and it didn't seem to help, so put the old one back on. the gpm now is at 40 where it should be, after messing with the destroke valve, and we are using the tractor and it functions fine but you can hear the hydraulic pump kind of howling.... jd tech is stumped as to why its making noise
 

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Discussion Starter #12
still havent gotten thius tractor 100%, we used it all spring and now its gone back for more testing to see whats up. now they think the scvs at the back are leaking and constantly bypassing, making the pump labor to much .. will see i guess.
 

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Is your oil getting foamy? Have you still got 40Gpm? What is your lube pressure? What is your standby pressure? Have they done a charge pump flow test? Also have they checked hyd. flow at the pump and not going through the scv's? What does the noise sound like? Does the noise change when you use brakes and/or steering?

Have them take pressure line off of pump and make a hose to return to sump. Put a flow meter in line of that hose. You can verify it pump issue or reaction issue. You can crank that flow meter clear off and work the **** out of the pump to see if it is getting overworked.
 

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Discussion Starter #14
ok im not sure if i can answer all of those questins buts heres what i know
the pump sounds like its working way to hard, or almost like its starving for oil.
It is not starving for oil, its got lots of oil
It has lots of charge pressure, im told.
It has lots of gpm at the scvs im told. it raises implemtens fast that i know.
it does steer fine and the brakes work are fine
When i steer it makes a howling noise, when i raise and lower implement same noise.
Just idling u can hear the pump labouring. hard to describe the noise. sound similar to how a tractor sounds if it is operating low on oil. or working really hard

One thing i did in the yard tonight was take off the pressure line to the scvs, pointed it at the ground and started the tractor. oil shot half way across the yard i shut it off quickly and put it back on. the pump does put out a lot of pressure to the svcs. Next i took off the return line (the one underneath the pressure line, its a little bigger) and started the tractor. Oil also came out of that line, not with the same amount of pressure but it came out fairly quick. Nothing came out of the SCV block where i had taken the hose off.
Is that normal? i had though the return line shouldnt have pressure at all. could there be a valve or something stuck in the hyd oil filter housing where my return line goes to, that would cause that, or is it normal? I also wasnt sure if oil would pour out of the scv block or not. but it didnt

The tractor goes back to jd in a few days, im just trying to wrap my own head around this problem. i was told by jd that some filings or something could have gotten stuck in a valve somewhere letting a lot of oil bypass. that hyds filter seems like the one place where a lot of large hoses meet.
 
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