(quoted from post at 06:12:45 05/11/19) Hi, you are correct the hydraulic system is setup like a 2444 where it uses the trans/diff as the hydraulic reservoir. I have never worked on one of these systems but it is a hydraulic system.
Where is the screeching sound coming from the pump area or the hydraulic control valve area? If the screeching is coming from the hydraulic control valve it could be something is tripping the relief valve.
Please post a picture of hydraulic control valve and the plumbing into it.
It sounds like the hydraulic pump is sucking air or the suction filter is clogged. Make sure the transmission is over full, check the suction line for leaks, clean or replace the suction filter.
Does the bucket cylinders do the same thing? Can you switch the hydraulic connectors for the bucket with the boom and see if the problem is in the hydraulic control valve?
It's pretty hard for me to nail down where exactly the sound is coming from. The noise and violent jerking happens to both the lift and bucket cylinders, in both directions. The only time it does not happen is if I push the lift control lever all the way past the detent and let the loader drop, it's not using any pressure at that point, so it drops smooth.
I made some videos. First one is operating the lift, second the bucket. At the end of the second vid when the loader is dropped, that's with the lever pushed past the detent.
https://www.youtube.com/watch?v=57cOcZvzuYw
https://www.youtube.com/watch?v=C6-4RgKVSWE
If you can't hear the squealing, just look for the camera shake, that's when it happens.
As far as the suction circuit. I had that all apart, new suction filter. I replaced all the hose sections in the suction circuit between the various hard lines, pretty sure I used all new hose clamps too.
Here are some pictures of the control valves:
https://imgur.com/WuPFi8n
https://imgur.com/nKkdRrv
You can see here the oil gets full of bubbles, I took a small sample and after about 30 minutes the oil is all cleared up.
https://imgur.com/LViRynF
This loader has been doing this since the day my Dad bought the tractor ~16 years ago. The HYD oil was always milky, always had water in it. We'd do a full change and it was back to milky in no time. So 3 years ago I pulled off the lift cylinder housing and went through everything. New gaskets, O-rings, suction circuit hoses, everything. I thought that if I could remove the water from the oil and keep it that way this problem would go away.
I finally discovered the source of the water was from the thin steel used on the suction/return line cover plate on top of the lift housing. This add-on required to operate the front PTO mounted pump was squeezing the gasket by each bolt and deforming the cover, allowing rain and snow melt to seep down into the lift housing.
I solved that problem by making a stiffener bar with set screws and jam nuts to force the cover plate flat to the gasket in the area it was deformed. See this pic:
https://imgur.com/YzwCani
They needed to use thicker steel for that cover plate or more bolts, poor design...
So, I solved the water in oil issue, but not the air/cavitation issue.
I mean, the only way you can get air bubbles into the oil is if the pump is sucking air along with oil correct?