Case Hydraulic Pump

[ih78]

What should the RPM be on the shaft that drives the hydraulic pump on a case 400? The hydraulics got weak and would not lift checked the pressure and it was 500 psi at full throttle. The system has been flushed, new fluid, new filters, new pump, pressure relief valve changed and the hydraulic float valve assembly rebuilt and the hydraulics still will not lift and the pressure is still 500 psi at full throttle. Do not not know what else to do but check the RPM of the shaft that drives the hydraulic pump or is there something that I have missed?

 

[EliG]

Assuming this is a big 400 with the round nose the hydraulic pump should turn at the same speed as the engine. The shaft that drives it is coupled to the flywheel by a splined shaft. Check the rpm of the pto because it is driven by the same shaft as the hydraulic pump. Although rare the shaft that drives them can break. Did you replace the orings behind the pump when you had it out? They can crack a allow the pump to suck air. Is the coupler, the round disk with the square blocks on each side, between the pump and drive shaft present and engaged in both shafts? Although rare it is possible to break the coupling. I have also had it fall out when installing the pump. There is also a screen on the inlet to the pump that could be plugged. If you take the hydraulic filter out you can see it on the left side of the filter opening.

Good luck.

Eli