Thank all of you for the welcomes. I hope to not wear them out. 2006 4120 PowerReverser open station with 228 hours. Original new purchase... mostly used to finish mow church ball fields and uproot small trees. Ran fine when parked, then bucket began to buck and became sluggish. Changed the spin on filter, cleaned the sump screen, 10 gal of Low-Vis and it ran all functions for about 30 seconds. Inline steering filter was clean. Stopped moving, no bucket, no rockshaft, no PTO and steering is ~binding. Most info says fluid/filters will fix this problem. I did lift the front end to burp steering and prime the system. Normal hydraulic service interval is 400 hours. NO metal in the screen, just aged fluid.
The real clue here is that the hose coupling at the pump manifold partially collapses upon starting the tractor. The 1- 1/2" pipe is clear, the sump is clean, if the filter was clogged the bypass would allow fluid to the pump -- it was free and pops off at 7 PSI resistance and JD parts provided me a replacement filter in case the first was defective.... same thing. Obviously, the pump is not defective since it is asking for more fluid -- evidenced by the collapsing coupling. I did add additional clamps to the hose, but if it was cavitation (sucking air), it would not collapse: it would whine. I know someone in here has heard of or encountered this phantom trouble... I did work the SCV and lift to exhaust all old fluid before change.
Is it possible that the PTO relief valve could vent more fluid than the pump can provide, or am I a victim of airlock and heading the wrong direction? Anyone know of a step-wise bleeding system in this situation? I thought this was self priming and BTW, the case vent is open - no dirt dobbers... I appreciate any input as I am dead-in-the-water where it sits and desperately need before winter.
Thanx in advance - FF