John Deere 300B hyd problem. Pressure Control Valve Orifice???

[Garrie Nolting]

Im having intermediate loss of hyd pressure for the loader and hoe. Cleaned suction screen, changed fluid. I understand the Pressure Control Valve (AR65882) can cause my problem and have removed it and cleaned it. Inside there is a cup shaped part that the parts manual calls an orifice, however mine does not seem to have a hole in it. Looks like it might have been "hammered" shut. My question is,,, does anyone know if this "orifice" actually should have a hole in it and if so how big does the hole need to be?

 

[Tx Jim]

Welcome to TBN
Did you change hyd filters? AR65882 is designed to give priority hyd pressure to steering. Sorry but I can't remember the answer to your question about the lack of hole in the orifice but IIRC it had a tiny hole in it. Many things attribute to closed center hyd pumps loosing pressure. Lose of pressure could be from lack of flow of trans pump to frt pump as front pump has no ability to suck oil from sump. An internal high pressure leak can rob frt pump of pressure also. With engine/hyd system at operating temp check for unusual higher temp of hyd function with a laser therm. Have you checked to be sure hyd filter relief valve isn't stuck open?

 

[Garrie Nolting]

Welcome to TBN
Did you change hyd filters? AR65882 is designed to give priority hyd pressure to steering. Sorry but I can't remember the answer to your question about the lack of hole in the orifice but IIRC it had a tiny hole in it. Many things attribute to closed center hyd pumps loosing pressure. Lose of pressure could be from lack of flow of trans pump to frt pump as front pump has no ability to suck oil from sump. An internal high pressure leak can rob frt pump of pressure also. With engine/hyd system at operating temp check for unusual higher temp of hyd function with a laser therm. Have you checked to be sure hyd filter relief valve isn't stuck open?

Yes I changed both hyd filters. If the filter relief valve was stuck open wouldn't the lack of pressure be continuous?
When I first got the machine I dug a few holes to test it out and it seems to be fine. Then I replaced most pins and bushings in the hoe, changed the oils\ and filters, replaced a couple cylinder hoses. Then when I tried to actually use the machine it loses pressure after raising the loader about 8-10 times in 3mins. I changed the oil again due to what appeared to be some water contamination and it worked as it should for an hour. Then back to the same problem. Would milky oil cause the lose of pressure?

 

[Tx Jim]

Closed center hyd's can be ornery to diagnose. Operating hyd's can deplete oil in reservoir by radiator then unless trans pump refills reservoir frt pump can run out of oil. From viewing BH parts catalog I also saw several relief valves on BH control valve that any 1 or more could be causing loss of hyd pressure if not holding correct stand-by pressure. Can you disconnect(isolate) BH hyd's from tractor & then operate FEL? My knowledge of JD industrial tractors hyd systems is very limited due to the fact that was employed by an "Ag only JD dealer" from '66-'87