I recently borrowed a ford 555d Backhoe and the hydraulics are very slow (the loader and backhoe) i have replaced filters and there is plenty of fluid in the reservoir. I have been trying to do research with little to no luck. The Hydraulics are hesitant and slow with little to no power. You can hear the pump trying to do something, but nothing happens. I've noticed if you hold a lever back (to raise the backhoe) idle the machine all the way down and rev it back up it will make the backhoe raise at normal speed for a split second than back to be slow once again. Also you CAN NOT lift the boom and dig at the same time. Any help would be greatly appreciated!
This is a general guess, I don't know that machine. All the other symptoms apply to any weak hydraulic pump, but it working for a second hints at being a supply problem to the pump, ie air leakage into the suction side, collapsing rubber suction line, cavitating pump, clogged suction screen... How does the fluid look after doing this for a few minutes, and before doing any work? What does it do if you operate it at slow idle? any difference in the noise?
noisy pump some times spline shaft is slipping from engine to pump,,,,also could be low of hyd fluid from storage tank to the pump filter/strainer and all the things Delmer suggested
broken spring on the pressure relief valve?