830 Hydraulic problems

[Dan in North Houston]

I have a 1974 3 cylinder 830 that I picked up for a brush-hog tractor. I knew it would need some work, but it was not in bad shape for it's age. Hydraulic pump started giving some problems, there was about a 10 second lag from the time you lifted the control lever until the arms started moving. Then it started to get weak, it would not lift the 3 point arms at all after the oil got warm. Ordered a new hydraulic pump and installed it. That was an ordeal, since the old pump was replaced by a different model that has the ports located slightly different. Hydraulic shop was able to cut and re-weld the hydraulic lines so that everything fit. Installed the pump today, started the tractor and the 3 point arms worked as they should. I tried them several times, and they worked flawlessly. Shut it down to continue installing the air cleaner, etc. Started it again and nothing. No lift arm action at all. I verified that the pump is turning. I don't have the proper fitting to test the hydraulic pressure at the test port. I believe I'm getting some hydraulic action from the power steering and brake response, but hard to be sure. Both the brakes and the power steering needs rebuilt, that is next on the list. i have cycled the lift controls numerous times, and tried different settings on the draft control. The tractor does not have any remote ports. The hydraulic lock screw under the seat is not causing the problem. I took it for a drive, and at some point, I noticed that the 3 point arms were up. I have no idea what I did to get that, and I've not been able to get them to rise again.
Any ideas on where to start? I suppose the rear hydraulic system needs rebuilt. Maybe the new pump had so much pressure on the old system, something let loose?
Any troubleshooting hints would be appreciated.

 

[Tx Jim]

If you didn't perform good hyd diagnostic procedures before removal of front pump it will surprise me if old pump is bad.

JD 830 utility tractor brake valve reservoir is supplied oil by trans pump & power steering operates from front section of hyd pump while 3pt is provided pressure oil from rear portion of the hyd pump.

Did you change hyd filter & check/clean the hyd oil suction screen prior to changing pumps?? I suggest to check to be sure hyd pressure relief valve is operating is seating. Also check to be sure hyd oil filter relief valve items 18-20 is not stuck open in trans case.