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Dan, Technician
Category: Construction and Road Equipment
Satisfied Customers: 5297
Experience:  17+ yrs. shop and field experience with all major brands of heavy equipment and trucks - 1995 WyoTech graduate.
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J D 790 ELC track . All hydralics suddenly became jerky.

Customer Question

J D 790 ELC track hoe. All hydralics suddenly became jerky. Like the controls are turning in and off. If you hold the bucket curl it will curl then stop then curl and so on. Tracks are the same. You can hear the engine load then release and run free and if you hold the control untill the end of stroke the engine will load up until you release the control. Has normal hyd power. Seems like the control is pulsing. Hyd filters are good. Thanks
Submitted: 2 years ago.
Category: Construction and Road Equipment
Expert:  Dan replied 2 years ago.
Hi my name is Dan. I will be glad to try to help. The symptoms you are describing point to most likely a pump/pump control problem or a relief valve sticking in the main control valve. Check the reliefs for metal/debris or damaged o rings causing them to stick open creating a loss of pressure in the circuit. If the reliefs check ok, check the hydraulic filter closely for fine metal looking like metallic glitter indicating a pump or component problem occuring. If clean the next step is to check the system pressures and compare them to OEM specs and also to see if the pumps are getting signal pressure to put them into full stroke. Check the pilot strainer in the pump compartment for metal as well. Let me know.
Customer: replied 2 years ago.
Both filters are clean. Which set of valves is the main control valve? Is it the one directly behind the swing motor or on the side?
Expert:  Dan replied 2 years ago.
Thanks for the update. It is the large valve body behind the swing motor between the swing motor and engine. The relief cartridges are threaded into the valve body on each function. They will have adjustement screws on the top with jam nuts. Do not play with the adjustment as you will then need test guages to reset the pressures. I just remove the whole assembly to inspect for debris holding them open and for cut or damaged o rings. You will lose oil so befor removing a relief wiggle the levers with all atatchments on the ground and release the tank pressure. You can pull a vacuum on the tank fill with a vacuum pump to prevent oil loss or you can just have a drain pan under with clean rags or plastic plugs if available to slow down the oil
Expert:  Dan replied 2 years ago.
Let me know. I will log in as I am able for follow ups and help any way I can.
Customer: replied 2 years ago.
I will check all tomorrow including pump pressures
Expert:  Dan replied 2 years ago.
How did you make out with your pressures? Let me know

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