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I have a John Deere 120C that has a hydraulic problem. The…

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I have a John Deere...
I have a John Deere 120C that has a hydraulic problem. The function for extending the jib boom out is very slow, but all other functions are fine.
Submitted: 10 years ago.Category: Construction and Road Equipment
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Answered in 1 hour by:
7/26/2012
Mechanic: Dan, Technician replied 10 years ago
Dan
Dan, Technician
Category: Construction and Road Equipment
Satisfied Customers: 14,844
Experience: 17+ yrs. shop and field experience with all major brands of heavy equipment and trucks - 1995 WyoTech graduate.
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HeavyEquipmentTech :

Hi my name is Dan. I will try to help. It sounds like you have a possibly relief valve or control valve problem. Check your oil level and your oil and filter for signs of metal and debris ( signs of a failed pump or component). If you find any metal in either, then you will need to clean out and flush your entire hydraulic system and repair your failed pump/ component. Check the control valve spool and relief valve on that circuit to make sure it moves freely and is not hanging up or sticking in its bore. Also check for debris that could be hanging up your valve. Pressure gages are also recommended to check your pressure on that circuit to verify it is within spec.. If so and that is the only function that is running slow then your hydraulic cylinder seals could be bypassing inside your cylinder. You could try swapping the lines from another function to see if it moves the problem to that function. If so, then you know the problem is in or before the valve. I hope this helps. Thanks for using JA

JACUSTOMER-0igd967e- :
HeavyEquipmentTech :

Hi.... it seems you may be having difficulties replying. I will switch to question and answer...

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Mechanic: Dan, Technician replied 10 years ago
Hi. Is this better????
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Customer reply replied 10 years ago
Dan, I have replaced the jib cyl with new and have placed guages at extend and retract ports and also on pilot ports I have 5000# main ports and 350# at pilots. I understand that there may be a combiner valve or a anticavitation valve on this function, if so where are they located. I also need to know what ramps up the pump because there is no change in cyl speed reguardless of engine speed.
Customer reply replied 10 years ago
Relist: Other.
no answer to reply
Mechanic: Dan, Technician replied 10 years ago
You have plenty of main pressure... The pilot pressure seems low to me.... Have you swapped the lines with another function at the valve as I mentioned in my origional post??? Let me repost my origional answer as I see there may have been some site difficulties....Hi my name is Dan. I will try to help. It sounds like you have a possibly relief valve or control valve problem. Check your oil level and your oil and filter for signs of metal and debris ( signs of a failed pump or component). If you find any metal in either, then you will need to clean out and flush your entire hydraulic system and repair your failed pump/ component. Check the control valve spool and relief valve on that circuit to make sure it moves freely and is not hanging up or sticking in its bore. Also check for debris that could be hanging up your valve. Pressure gages are also recommended to check your pressure on that circuit to verify it is within spec.. If so and that is the only function that is running slow then your hydraulic cylinder seals could be bypassing inside your cylinder. You could try swapping the lines from another function to see if it moves the problem to that function. If so, then you know the problem is in or before the valve. I hope this helps. Thanks for using JA
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Customer reply replied 10 years ago
no signs of metal in oil or filters, was wondering what is that ramps up the pump, there has to be a signal/load sense that tells the pump to increase flow, that or anti cavitation valve or combiner valve to increase speed. There is also electrical solenoids on the pump controler, need to know if they need to excite to ramp up pump, if so when/how?
Mechanic: Dan, Technician replied 10 years ago
What is the SN of your machine? I recommend obtaining a schematic and pressure specs for your machine serial number so we have detailed info on your system otherwise we would only be guessing. Depending on your particular pump, you will have signal lines to your servos that will stroke the pump between one and two pump flow as your functions are split between two pumps. I should have the pressure specs once I get the SN. I will do my best to help you and if there is any information I cannot provide you, I will try to get it for you.
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Dan
Dan
Dan, Technician
Category: Construction and Road Equipment
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Experience: 17+ yrs. shop and field experience with all major brands of heavy equipment and trucks - 1995 WyoTech graduate.

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