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

[David VanName]

I recently put my jd 855 compact tractor back in use. It ran fine for about 10 hours and then the 3 point hitch arms began to pulsate when in the lift position with an implement on. I had split the tractor to have some welding done on the rear differential front cover, so all the linkage was taken apart, as well as the front cover removed from the differential. This exposed all the gearing forward of the differential. I have looked at linkage as a possible cause so far. It is possible that the pulsating was there right from the moment I put it back together and I would not have noticed it because I hadn't used any implements other than the bucket.

 

[murphy1244]

maybe dirty filter and fluid.

 

[hosspuller]

Likely leakage of the piston. Fluid leaks, piston drops, system pumps it back up ... repeat, repeat = pulsation.

Also it may not be the piston, but could be anything in the fluid path... valve, housing, etc

 

[Mechanos]

You didn't mention the engine RPM where you are noticing the pulsation. As mentioned above, most likely leakage around the rockshaft piston seals. My 955 will do this with a heavy implement raised at low RPM. If I raise the engine RPM (and thus increase the flow from the implement pump) the increased flow overcomes the leakage rate and the pulsation stops.

 

[David VanName]

With the rock shaft in the lowest position no load, there is no surge. The more lift and/or load the worse the surge. The more the rpm the more the surge.

 

[JerryK]

My JD 2240 started doing that. I had to replace the valves/seats in the 3pt controls and put new springs in. Lots of the springs were out of specs and I just replaced them all...stuff gets old over time. Put a new seal in the large 3pt piston whilst I had it apart, but it was probably not leaking.

 

[Mechanos]

I do remember a #100 mesh screen filter in the rock shaft control valve assembly. You might try cleaning that filter screen off and reinstalling. What you are describing does not sound like leak by on the piston seals.

 

[David VanName]

Thanks for getting back to me. Your last post has put a little hope back into my sorting this out. I will get back to everyone as soon as I get a chance to tackle it again. That will most likely be Tuesday night.

 

[David VanName]

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.

 

[murphy1244]

sounds like a relief valve is stuck open. You may want to post this in the Hydraulics forum so JJ can see it.