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From what you describe, I would say your pump is OK, but it is starving for oil. Look at it this way--take your loader for instance. You've got plenty of pressure resulting in good loader power. This means the pump is not bypassing internally. At low RPM, the pump does not move much oil, therefore it does not require much oil coming in on the suction side of the pump. On the backhoe, the smaller cylinders don't require as much oil (smaller cylinder volume)as the larger ones, so the reduced volume output of the pump will run these OK. However at high RPM, the pump moves a lot of oil (12GPM for a standard equipped 460), therefore a lot of oil has to be supplied at the suction side or the pump will cavite (suck wind) and introduce air into the hydraulic system on the pressure side of the pump. This introduced air takes up space where hydraulic oil should be. Since air is compressible, your loader is floating down--the loader's backforce is compressing the air. Sure sounds like you've got a plugged filter/suction screen and/or not enough hydraulic oil in the resevoir. MNScott: thanks for recommending our site.
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