JD 310E backhoe transmission system pressure study?

[JL Sargent]

I connected a 300 psi gauge to the System Pressure port today and I have 230 psi at this port after I crank the tractor. This seems to be normal. Releasing parking brake momentarily drops this pressure to 150 for a second, but then its right back up to 230. Then after 10 minutes or so of moving the tractor around I can watch this pressure drop pretty quickly to sub 100 psi and by design the parking brake is applied with the loss of hydraulic pressure. Then I can turn off tractor and let it sit for a few minutes (5 minutes at the most) and recrank and I then have a strong 240 psi on my gauge? It can stay in this 230 to 240 range for quite a while (20 to 30 minutes maybe) before repeating the scenario. Any ideas? If I couldn't restart tractor and get things back to normal, I would suspect the transmission charge pump. Pressure regulating valve maybe? Your thoughts appreciated.

 

[JL Sargent]

This ended up being a clogged screen on the charge pump pickup tube. I drained the trans fluid, removed the charge pump, ran a bore scope down the pickup tube and could see the clog. I back flushed this screen for several hours with diesel fuel/air gun and was able to clean it about 90% I'd estimate. After putting the tractor back together, system pressure is 250 psi and all is working properly.