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Recently acquired a JD 2640 with a Kelly 800 loader that has hydraulic problems. Changed the oil, cleaned the filters, and got the air out of the system. Hydraulics work great at startup at high RPM only, but as soon as you drop the RPM hydraulics start shuddering or fail totally. I changed the oil, cleaned the filter, and the results are same. My grandpa suggested that the hydraulic pump might be worn out. He said that the oil is pumped by paddles with little cups in them. He said that with age the cups wear out, which means that the pump can't pump oil at idle speed and will only be able to spin fast enough to move enough oil to move the loader at high RPM. Is this possible? If so, can i replace the pump? If so where is it located? Any help will be appreciated. Thanks.
 

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Recently acquired a JD 2640 with a Kelly 800 loader that has hydraulic problems. Changed the oil, cleaned the filters, and got the air out of the system. Hydraulics work great at startup at high RPM only, but as soon as you drop the RPM hydraulics start shuddering or fail totally. I changed the oil, cleaned the filter, and the results are same. My grandpa suggested that the hydraulic pump might be worn out. He said that the oil is pumped by paddles with little cups in them. He said that with age the cups wear out, which means that the pump can't pump oil at idle speed and will only be able to spin fast enough to move enough oil to move the loader at high RPM. Is this possible? If so, can i replace the pump? If so where is it located? Any help will be appreciated. Thanks.
I understand you changed the filters. Does this have a suction screen on the oil pick up side in the reservoir?
 

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One needs to perform good hyd diagnostics before considering replacing frt hyd pump. Many closed center pumps have been replaced only to determine that replaced pump was not at fault. Power steering,ft end loader & 3 pt control valves have all been known to cause closed center hyd not to operate correctly plus there are several other causes for hyd system failures not mentioned.:gizmo:
 

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This tractor does have a suction screen inserted from the bottom right side of the reservoir if standing at rear of tractor. Could anyone suggest what to check first? I've never worked with big tractors or hydraulics and this seem like a big question for me. Thanks.
 

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This tractor does have a suction screen inserted from the bottom right side of the reservoir if standing at rear of tractor. Could anyone suggest what to check first? I've never worked with big tractors or hydraulics and this seem like a big question for me. Thanks.
Did clean this screen? If so, how bad was it? If it was real bad, I would also clean the transmission filter bypass valve to make sure it is not stuck partially open

Did you change, not clean the transmission filter?

Does tractor have Reverser or HI-Lo transmission? Transmission pump supplies them and they could be leaking internally robbing the front pump of oil flow.

Does engaging the PTO make a difference? Also operated by transmission pump. I had a internal PTO steel line break and it created a leak to sump and my other hydraulics would not work.
 

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I have changed the oil multiple times and cleaned screen all the times. I also changed the hyd oil filter. It was partially, but not totally clogged. I have heard about cleaning that valve, but i don't quite know where to find it. I'd probably need a parts diagram or something. This tractor has hi-lo but as far as i can remember it did not affect ground speed. This probably indicates an internal leak? Engaging pto does not affect hyds performance. Thanks again.
 

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I have changed the oil multiple times and cleaned screen all the times. I also changed the hyd oil filter. It was partially, but not totally clogged. I have heard about cleaning that valve, but i don't quite know where to find it. I'd probably need a parts diagram or something. This tractor has hi-lo but as far as i can remember it did not affect ground speed. This probably indicates an internal leak? Engaging pto does not affect hyds performance. Thanks again.
Go to jdpart.com to see parts diagrams. The transmission oil filter relief valve is right near the top of the oil filter. Has a hex plug you remove to access it.

You should, when shifting the HI-LO, experience a change, almost the same as shifting to a lower gear (HI to LO shift). See if being in HI or LO makes a difference for your hydraulics, that might tell which part of the HI - LO is bad, but if it's not getting oil from the transmission pump, it (HI - LO) could be OK. I would start with the filter bypass valve next.
 

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Ok, i have finally pulled out the relief valve. It is all assembled together as one part. As far as i understand the parts diagram is an exploded view. Should i disassemble it to clean it up inside? Thanks again.
 

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I think it would be good to disassemble the valve to be sure there's no debris in the valve.
Check that part 5 moves freely against the spring. It would not hurt to take apart and clean. There is probably a "free length" for the spring that can be checked too.
 
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