I'm back again! I appreciate all the help I received solving my last issue with the John Deere 490e boom being weak . My issue now is that the thumb became weak today and a couple of days ago after about an hour of operation. It would not hold my grading beam any longer. The hydraulic system was around 150 fahrenheit, so not too hot. Thumb up seems to be fine and strong, hitting the system relief pressure of 5400. I am not sure what the pressure settings are supposed to be for the thumb, the manual doesn't say. When the machine is first turned on and the thumb is operating correctly, thumb down has a pressure of 2800. When the issue occurs, I am only getting around 200-800 psi of pressure. I noticed the thumb hydraulic lines seem to "dance" more as well when this happens. Here is a video demonstration of the issue: https://photos.app.goo.gl/rYB8GBBeE3o2G3gK7 Since the boom down issue was fixed by replacing the circuit relief valve, I have had to replace a couple of hydraulic hoses that burst as well. Here is the most recent one, I am not sure if it is related to the thumb: I am wondering if I have some sort of hydraulic system contamination as this issue is similar to the boom down issue? Hmmm... The manual doesn't say a lot about the auxiliary setup or psi settings, here is what it says about the auxiliary valve:
I am going to assume you have a Deere factory auxiliary plumbing . kit installed. The kit came with (2) circuit relief valves. Generally with a thumb , the cylinder barrel end circuit releif valve is set to approx 2500 - 2800 psi. It is set low so the thumb cylinder will retract when ever the bucket curling forces against the thumb tines.
Thank you. I see the parts page also says there are two circuit relief valves. I have a screenshot below from the manual with what I believe are the valve locations, is this correct? My plan is to swap these two valves and see if the problem shifts. Do you agree this is a good approach?
I circled in red the location of the relief valves in your screenshot below. The 2 plugs were removed and relief valves installed in their place. Swapping relief valves is a good approach for testing purposes. Just be careful not to force on the thumb when curling the bucket.
Thank you! I swapped these valves and now the weakness has moved to thumb up. I could live with it since thumb up is not a function I need a ton of power on, but I am going to buy a replacement anyways and get it working. I think the auxiliary relief valves are the same thing as the main function relief valves right? Also, if you know a good shop I could mail the originals to, let me know. I could try to rebuild them myself, but I don't know any of the specs to expect from the springs...?
Some of the dig function circuit releif valves have a built in anti cavitation feature. I am not certain the auxiliary reliefs have that feature. The auxiliary relief valve part number is in Post #2. When all is said and done don’t forget to adjust the pressure down in the circuit relief valve that is in the work port connected to the thumb cylinder barrel end.