Ford 4000 hydraulics?

The most likely cause would be that the pressure is set too high, you will have to fit another pump but the pressure will have to be checked using a flow meter/ pressure guage kit,the pressure should be 2400 PSI, the flow meter has to be connected to the external service pipe or spool valve whichever is fitted and returned into the backend the flow on the meter can be shut down gradually and if the pressure rises above 2400 PSI, the releif valve must be removed from the pump and shims removed as necessary until the correct pressure is acheived.

Para Handy
October 2009