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  1. #1
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    1980 AC 5020

    Default How do you diagnose weak/slow FEL?

    I've got a 1980 AC 5020, only 800 hours on it. To me it seems to have a weak FEL, and it's slow. I'm just trying to pickup some manure and it has a hard time doing that. How can I diagnose the hydraulic system?

    I've thought about installing a pressure gauge somewhere in the system, would that tell me much? It doesn't have power beyond, so I thought the pressure gauge could go between the hydraulic pump and the FEL control valve and that give me a good reading of the full pump pressure available to the FEL. Am I heading in the right direction?

    How could I test the pressure relief valve? Is there a way to install the pressure gauge and get a reading of the pressure relief valve release setting?

    I've changed the hydraulic/transmission fluid, so I hope that's not the problem. The fluid is supposed to meet the specs for the tractor.

    I'm looking for generic techniques that don't have to be too specific to this tractor. I have manuals, both service and parts if there is anything that might help in there.

    Thanks,
    Monte

  2. #2
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    Default Re: How do you diagnose weak/slow FEL?

    Raise the boom up all the way. Disconnect the non-raise hydraulic hose from the cylinder. Use the control to raise it again and hold it in the raising position. The pressure relief will bleed off the fluid -don't worry. If there is a significant amount of fluid coming out of the cylinder the packing is bad. Reconnect, lower the boom all the way and repeat on the other side holding it in the down position. Redo for the bucket if you want to check it.

    You can buy a 0-5000psi gage for 15 bucks and some T's for 20 bucks or less. Put the gage on the raise port of the boom. Then raise it all the way and hold it until the pressure relief activates. That is your max system pressure That should be about 2500 psi (You should look up the correct number). You may just have a weak relief valve.

    jb

  3. #3
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    Default Re: How do you diagnose weak/slow FEL?

    Quote Originally Posted by john_bud
    Raise the boom up all the way. Disconnect the non-raise hydraulic hose from the cylinder. Use the control to raise it again and hold it in the raising position. The pressure relief will bleed off the fluid -don't worry. If there is a significant amount of fluid coming out of the cylinder the packing is bad. Reconnect, lower the boom all the way and repeat on the other side holding it in the down position. Redo for the bucket if you want to check it.
    I think I get what you are doing. Raise the loader, then disconnect the hose(s) from the non-pressure side of the cylinder(s) and open the raise circuit again to try and and see if there's "blow-by" in the cylinders.

    I'm not sure what you are describing here though, "The pressure relief will bleed off the fluid -don't worry."

    You can buy a 0-5000psi gage for 15 bucks and some T's for 20 bucks or less. Put the gage on the raise port of the boom. Then raise it all the way and hold it until the pressure relief activates. That is your max system pressure That should be about 2500 psi (You should look up the correct number). You may just have a weak relief valve.

    jb
    I'll give both ideas a try. To me, something is weak in the system. Even the bucket is weak just tipping back from flat after loading it up.

    Thanks,
    Monte

  4. #4
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    Default Re: How do you diagnose weak/slow FEL?

    Usually in the loader valve, but sometimes in a central location on the tractor (or both) there is a spring loaded device. The spring pushes against a ball or a plunger that closes off a fluid path back to the tank. The ball or plunger is moved on one side by the system pressure and held against that pressure by the spring. As the spring ages, it is less forceful, less able to resist the hydraulic pressure and keep the relief path to the tank closed. That is a discription of both what a relief valve is and how it works.

    When I said don't worry ==> if you didn't know about the relief valve you might think that the pump is dead heading pressure and might damage either itself, a hose or the cylinder. Dead heading a pump will cause permanent damage to the pump, unless something else is damaged first! Holding the control against the stop and letting the relief valve operate for 5 seconds is not a problem. Holding it for a long time will heat the fluid up as it is forced across a small relief port. Sometimes you can use that fact to find a stuck open relief valve by operating the tractor for a few minutes and feeling for the hot spot.

    It sounds like you have low effective system pressure. Either you have a relief valve that is stuck open, set wrong, has a weak spring (effectively set wrong) or a pump that needs rebuilding. I doubt that all the cylinders are bad, but that does happen!

    jb

  5. #5
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    Default Re: How do you diagnose weak/slow FEL?

    Quote Originally Posted by john_bud
    Usually in the loader valve, but sometimes in a central location on the tractor (or both) there is a spring loaded device. The spring pushes against a ball or a plunger that closes off a fluid path back to the tank. The ball or plunger is moved on one side by the system pressure and held against that pressure by the spring. As the spring ages, it is less forceful, less able to resist the hydraulic pressure and keep the relief path to the tank closed. That is a discription of both what a relief valve is and how it works.
    Thanks for that.

    When I said don't worry ==> if you didn't know about the relief valve you might think that the pump is dead heading pressure and might damage either itself, a hose or the cylinder. Dead heading a pump will cause permanent damage to the pump, unless something else is damaged first! Holding the control against the stop and letting the relief valve operate for 5 seconds is not a problem. Holding it for a long time will heat the fluid up as it is forced across a small relief port. Sometimes you can use that fact to find a stuck open relief valve by operating the tractor for a few minutes and feeling for the hot spot.
    Makes sense, I never thought of testing the relief valve for heat.

    It sounds like you have low effective system pressure. Either you have a relief valve that is stuck open, set wrong, has a weak spring (effectively set wrong) or a pump that needs rebuilding. I doubt that all the cylinders are bad, but that does happen!

    jb
    The relief valve is on the outside of the transmission, and there's a test plug/port shown in the service manual that can be used to install a pressure guage. The spec's for this system are 5.88 gal/min at 2700 rpm, and 1710 psi relief valve setting at 1285 rpm. Can you tell me if there's a way to discern a weak pump from a weak relief valve without removing and bench testing the pump? Assuming I get a low pressure reading.

    And I guess another basic question would be should I expect much lifting power and "speed" from this system, given the 5.88 gal/min and 1710 psi spec's?

    Monte

  6. #6
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    Default Re: How do you diagnose weak/slow FEL?

    you would need a flow meter to check the pump for flow the spec for it would be around the 5.88gpm you would check it at no pressure and them at relief pressure 1750psi then you will need to know what loss is alowed. remember the speed is flow where power is pressure what you have for both is also affected by the size of the cylinders and hoses.

  7. #7
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    Default Re: How do you diagnose weak/slow FEL?

    Quote Originally Posted by Dirthog
    you would need a flow meter to check the pump for flow the spec for it would be around the 5.88gpm you would check it at no pressure and them at relief pressure 1750psi then you will need to know what loss is alowed. remember the speed is flow where power is pressure what you have for both is also affected by the size of the cylinders and hoses.
    Ran a quick search on flow meters, about $150 for what I thought I would need. I guess a permanent flow meter and pressure gauge would be sort of useful, longterm, I suppose.

    Monte

  8. #8
    Veteran Member Hooked_on_HP's Avatar
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    Ford 1900 FWD Kubota F2100E

    Default Re: How do you diagnose weak/slow FEL?

    Monte hook up the heavyest attachment you have to the TPH and see if it lifts it quickly. If the TPH works fine the problem is in the loader control valve. It could be a weak pressure releif or a seal in the spool. When you changed the fluid did you service the filter.

  9. #9
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    Default Re: How do you diagnose weak/slow FEL?

    Quote Originally Posted by Hooked_on_HP
    Monte hook up the heavyest attachment you have to the TPH and see if it lifts it quickly. If the TPH works fine the problem is in the loader control valve. It could be a weak pressure releif or a seal in the spool. When you changed the fluid did you service the filter.
    Heaviest I've got is a 5' box scraper with hooks. It seems to lift that just fine, speed wise. I pulled the filter out, it was clean.

    So, might the control valve have it's own relief valve? I don't have a manual for the FEL, it's an Allis Chalmers unit, don't know anything about the control valve. I've been thinking about replacing the control valve with a joystick unit instead of the 2 stick one that's on there now. And power beyond, so I can get rid of the diverter valve, I want to add a backhoe this year. Hmmm, got me thinking about it now. It's money I was planning on spending eventually anyway, maybe I should look closer at the control valve first.

    Should I try and lift some weight with the TPH? Would that be an indicator of the system "power"?

    Monte

  10. #10
    Veteran Member Hooked_on_HP's Avatar
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    Default Re: How do you diagnose weak/slow FEL?

    Monte, your control valve should have its own pressure releif valve. It will screw in to a port in the valve. They are usually about an inch and a half long. Sometimes it has a cover over it that unscrews so you can adjust it. You should have a pressure guage hooked up when you try to adjust it.

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