JD 4020 powershift hydraulic issues

I have a friend here in Australia that has this tractor -I haven't been out to see it yet - intermittently the hydraulics will quit - no power steering, 3 point, scv. park it for a few days and try it and everything works again - last week he used it for 2 hours and then the hydraulics stop working -if he revs it wide open the loader will lift slowly - I told him to change the oil and filters and clean the screen - he did there was some stuff on the screen but it wasn't plugged . he started it and drove it a short distance - the steering would work while driving - which is basically manual steering, but the transmission seemed to shift fine - he pulled the line from the valve block that goes to the main pump, and there was lots of oil flow - I got him to pull the stroke control valve and it and brought it to the shop - it all seems fine - he is going to install the stroke control valve tomorrow and adjust the pressure screw at the bottom to see if he gets some hydraulic response - with out testing pressures, it is hard to diagnose - he is thinking of replacing the main pump, but I am reluctant yet since it seems to be an intermittent problem. where else can he check before I am able to get to his place -I have the original service manual, and there are testing procedures - which includes testing the main pressure regulating valve - I don't have the proper fittings yet - any ideas?
 
Stand-by pressure needs to be checked and set at 2250-2350 psi. Many frt hyd pumps have been replaced only to find out that the hyd problem was somewhere else. Closed center hyd systems require good diagnostics. You can test stand-by psi by plugging a gauge in the rear breakaway coupling. Since steering has no to little hyd power I doubt pressure control valve is the culprit.
 
Hi Ken; certainly NOT the expert here but I'll throw in a couple of thoughts. I had a 2950 here a number of years back that would act like this even after a new stroke control valve was installed. When the hydraulics quit you would dial the destroke valve in, then out and all would be good. It eventually healed itself so I think the valve was hanging then freed up over time. Just an idea. Like Tx Jim says standby pressure is important but we all know we can get false reads of less then perfect working SCVs
You also said it has a loader....might want to see how its plumbed (independant valve or through SCV) as a leak in the independant valve would starve the system again just a thought.
I will come over and help you for free if you send the airfare, deal?
I know you will sort this one, let us know what you find,right?
 

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