3-Point Hitch 4310 3 point hitch

[drphilwoods]

Hi

I have been having awful problems with my JD 4310 3-point hitch. It will only stay up if locked in this postion. Otherwise if you lift it and let it go it comes all the way back down. So far I have changed the rate of drop valve, rockshaft piston ring and back seal. More recently my technican found debris in the HEMA rockshaft control valve and we have replaced this. John Deere technicians here in Saskatoon have not been that helpful. My techican is convinced the problem lies in this rockshaft control but we have now fitted 2 new ones and they both behave the same. The valve is attached to the rockshaft casing via 3 bolts and has 3 o-rings where it meets this casing. The valve has machined chambers and 1 valve at the front of the rockshaft control valve and 1 valve at the side. We are assuming these are pressure relief valves. The technician that is working on my tractor is convinced that hydraulic fluid should be maintained within this rockshaft valve and not behave the way it is. The valve is covered by a dust cover with no gasket which is why he is convinced of this. When we lift the 3-point hitch hydraulic fluid comes out the side pressure relief valve at extreme pressure and when the 3 point hitch is lowered hydraulic fluid comes out the front pressure relief valve at extreme pressure.

Any help please?

Regards
Phil

 

[dmp437]

We are assuming these are pressure relief valves

No need to assume, there is a Rockshaft System Componet diagram on page 732 of the Service Manual.
Did the service tech perform the "Rockshaft Lift Cycle Test" on page 750 and the "Rockshaft Leakage Test" on page 751?
Also check out the Rockshaft System Schematic on page 734 for a visual representation of how the componets are interconnected along with the "Rockshaft Theory of Operation" on page 744.
From the leakage test coupled with what has been changed already, the relief valve would be the next thing to check.