Hi Guys I changed the HyGuard, filter and cleaned the long screen cylinder next to the PTO. Everything looked fine. Filter didn't seem heavy, just a few metal fillings in the screen. Have starting it up it seems to act about the same as it did before I changed the oil and filter. Some think it is cavitation problem, but I do not hear any load banging or popping, etc.
Could there be a small air leak in the suction side of the system? Not sure how to check for that though!
OK. What you did means you don't have a cavitation problem. That's real good to know.
Yes, it could still be an air leak in the suction side. Or it could be a suction leak in the pump drive seal.
Look for a suction leak on the line from the sump to the pump inlet first. It's easiest.
Two general clues to a suction leak somewhere in the suction side are:
1. In the suction line, when the engine is off, you will find a few drops of oil accumulating on one of the suction line joints. Check the suction line between sump, filters, and intake to the pump. It should be dry. If oil is escaping when it isn't running, then it is sucking air when running. Look especially at any rubber hose to metal fittings.
2. A suction leak will often cause new hydraulic oil to look cloudy instead of transparent. If yours is cloudy after it runs for a few minutes then you may be seeing micro bubbles from a suction leak either in the suction line or the pump. Suck up an oil sample and put it into a jar for an hour to see if the cloudiness goes away. If so, it was micro-bubbles. ALL systems will have some cloudiness, and an otherwise good hydraulic system can handle some air. So this is not a real good test.
About the only other ways a hydraulic system can be weak and need full throttle to perform are all mechanical:
It could be a bad/stuck/broken spring in a pressure relief valve - usually found on the loader control. Or the same on the proportional valve that regulates power steering vs loader pressure. .
Or it could be a worn hydraulic pump.
None of those are the end of the world. Some cost more than others, but all are easy to replace.
You find those mechanical things by making up a pressure gauge and checking pressure at various places.
Look for a suction leak in the line first. Then a bad relief valve second. A real bad relief valve will squeal or rattle.
good luck,
rScotty