New Holland 555 Deluxe

[mayorpres]

I have a 1990 model 555 that just recently the boom and bucket will not operate. I have rebuilt the drive pump and changed the filters. Same problem. The transmission pump is working fine. When I move the machine forward or reverse the hydraulic light stays off, but when I try to lift the boom or bucket, the light comes on and immediately after release of the pedals, it goes off. I have read many threads about the wiring of the seat and safety controls, but this machine has had all of the wiring for the seat and seat belt off for many years. Could this be a relief valve issue or maybe a control valve? Any suggestions? Thanks

 

[Mike10]

I think you are on the right track with the relief valve. The hydralic pump is flowing oil or you would not be able to drive the unit. Whether it is up to specs is another question. The charge pressure oil comes from the return hydraulic oil from the control valve via a check valve. If the electronics was the problem you should hear the engine labor when the oil goes over relief. The only place for the oil to escape, in the volumn you are describing, is through the relief valve or a massive crack in the control valve. The only way to narrow it down for certain is to use a flow meter and guages.
Did you remove the screen from the standpipe next to the hydraulic pump and clean it? The hydraulic pump input hose is attached to the standpipe.