I am now just getting back to this tractor problem.
1. I cleaned the suction screen, which was about 20% clogged with black rubbery stuff. Hyd. oil was clean, no water or silver color. Did not fix problem.
2. I checked the transmission bypass valve- was clean
3. I installed pressure gauges on the main pump (which is a serial # tagged 2.4 inch pump)--I believe the right side top port is pump output and the lower port is feed pressure from the transmission. The output pressure immediately jumps up to 2200 psi,even at idle rpm, that's good, but the charge pressure was maybe 5 psi, or less. At high rpm, the output would stay nicely at 2200 psi, and the charge pressure would slowly creep up to 20 psi. When a cylinder was activated, the charge pressure drops to 0. After the cylinder action is stopped, the charge pressure will creep up to 1-5 psi. After about 10 minutes of running, the charge pressure drops to zero and the output pressure becomes erratic, ranging from 2200 to 0.
Before heating up, the machine has plenty of power for digging or loader lifting. After warm-up, it becomes slow, weak and erratic. I noticed the Hydraulic oil reservoir tank is empty after running, and had a slight suction when I opened it (tractor off). No sign of hose kinks or dents anywhere.
4. I felt all the backhoe and loader valves for temperature; all stay cool except the steering column, which gets noticeably hot within a minute or two of running. For years, the steering has always been a little quirky--occasional interactions between loader operation and steering, occasional no power steering with a heavy loader load.
Questions: 1. How does the pressure control (priority) valve work? Does it shunt transmission charge pump pressure to the steering gear, or does it send main pump pressure preferentially to the steering?
Would a bad pressure control valve cause the main pump charge pressure to be so low?
2. What about the heating of the steering column? Would internal leakage cause the low charge pressure? Does the steering work on transmission pump pressure or main 2200 psi pressure?
3. Is there a way to test the transmission oil pump independent of the steering, or to plug off the steering for testing?
I got a new stroke control valve and plan to change it, but that does not seem like it will cure the problem. Any other suggestions/
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