causes for pulsatiion in 3 point hitch of a john deere 855

[Mechanos]

Cleaned the #100 screen. There was a minimal amount of debris. But well worth the effort to inspect and clean. Replaced hydraulic fluid at same time. If I turn off the rate of descent valve for the 3 pt hitch under the seat the surging stops. With the valve open the surging is still present. If there is a little weight there is a little surging. More weight more surge. I have no oil being produced by way of a leak.

If you close the rate of drop valve completely with the engine running, you put the hydraulic system into relief (forcing the relief valve to open as the only path for hydraulic fluid to flow). You should hear the engine load increase when you do this and it should not be run for long in that position. The leak refered to is an internal leak... you would not see any oil leaking onto the ground.

 

[Tx Jim]

Sounds to me that the 3 pt control linkage is "hunting" or some call it "hiccuping". The control valve can't find "neutral" because of escaping oil. This could be caused from improper linkage adjustment,leaking rockshaft piston seal or leaking thermal relief valve.

 

[Tx Jim]

If you close the rate of drop valve completely with the engine running, you put the hydraulic system into relief (forcing the relief valve to open as the only path for hydraulic fluid to flow).

I disagree closing rate of drop screw just shuts of the return port on 3 pt control valve therefore keeping 3 pt at set height but in no way puts load on engine or sends hyd system into relief at least that's the way it is on the tractors I've been around. If ROD valve is barely open it controls 3 pt speed of decent.

 

[Mechanos]

I disagree closing rate of drop screw just shuts of the return port on 3 pt control valve therefore keeping 3 pt at set height but in no way puts load on engine or sends hyd system into relief at least that's the way it is on the tractors I've been around. If ROD valve is barely open it controls 3 pt speed of decent.

It does on the x55 tractors. With the stop valve closed and the rockshaft lever in any position except fully forward put the system into relief.

 

[Tx Jim]

Thanks for correcting me as I haven't been around a tractor that the hyd's operated like that.