Tractor Repair: Ford 4000 Hydraulics, rear axle, hydraulics

Question
I have a 1962 Ford 4000 (Gas - 4 cyl). The hydraulic, when in "lift position", bounces up and down badly, shaking the whole tractor. Changed the fluid, but not much help.  Is there a filter?  Any ideas?

Answer
There is no filter that I can see, but there is pick-up tube's in the bottom of rear axle housing that can be cracked.  The problem can be either the pump going south, pipe cracked or in your rockshaft valve or housing. If you have any aux hydraulics you can test pump flow. Otherwise run the hitch when it starts bouncing then check for foaming oil if it is not foaming then it is in your rockshaft valve or cylinder. Hope this helps