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cat 308e boom extends fully on start up and then drops when off

Discussion in 'Excavators' started by AUGUSTINO PALLADINO, Sep 28, 2021.

  1. AUGUSTINO PALLADINO

    AUGUSTINO PALLADINO Member

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    I have a 2012 Cat 308e with 3000 hours, for some time the boom would slowly fade down. Now when start up the boom extends fully on its own and loads the engine. when off or after it stalls it comes right down fully. Their are no fluid leaks.
    I am think its a valve just not sure where, joystick or on the motor?
     
  2. nowing75

    nowing75 Senior Member

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    sounds like the spool in the main valve is stuck open. Have had this happen on a dozer and i found metal holding the spool in the up posisition.
     
  3. AUGUSTINO PALLADINO

    AUGUSTINO PALLADINO Member

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    can I pull that valve or do I have to relive pressure first.
     
  4. Nige

    Nige Senior Member

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    Sounds like the spool that controls in the main control valve is jammed by something. Probably something from the boom cylinder that was creeping down before. Just hope for your sake it's a piece of something non-metallic or you could be in a whole heap of trouble.
    Make sure the bucket is on the ground and slacken the two hoses to the boom cylinder. That should relieve the pressure.

    I could post you an illustration of the inside of the control valve but to do that would require the machine Serial Number. there are 20+ different types of 308E.
     
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  5. AUGUSTINO PALLADINO

    AUGUSTINO PALLADINO Member

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    thank you I dont have the serial number with me.
     
  6. AUGUSTINO PALLADINO

    AUGUSTINO PALLADINO Member

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    it couldnt be the valve under the joy stick?
     
  7. Nige

    Nige Senior Member

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    Highly unlikely based on your original story. If the boom was coming down under its own weight prior to this issue it is highly likely that the seals in the cylinder(s) were starting to disintegrate. I think it is quite possible that a piece of seal has broken off and found its way back to the main control valve where it is jamming the spool. The main control valve is the first component in the circuit at which debris would arrive if it came from the cylinders.

    Below is an illustration why a Serial Number is important - and that isn't even the complete list............
    upload_2021-9-28_18-2-25.png
     
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  8. AUGUSTINO PALLADINO

    AUGUSTINO PALLADINO Member

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    Thanks for your info. Just got up to the property this weekend. The stick now wont go in or out. its hard to follow the hose to the valve, If you can help with letting me know which valve to go after first that would be extremely helpful. ser# GBJ01294
    Thanks
    Augie
     
  9. Nige

    Nige Senior Member

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    Boom control valve spool is #17.
    upload_2021-10-18_15-13-18.png
     
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  10. Nige

    Nige Senior Member

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    Here are the disassembly instructions for the control valve. They might assist you.
     

    Attached Files:

    Gary Layton and Vetech63 like this.
  11. AUGUSTINO PALLADINO

    AUGUSTINO PALLADINO Member

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    which one is the valve for the stick? I said boom, but its the stick that is the issue. cylinder on top of the boom.
    Augie
     
  12. Nige

    Nige Senior Member

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    There is a marked drawing in the attachment.
     
  13. AUGUSTINO PALLADINO

    AUGUSTINO PALLADINO Member

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    looks like #27?
     
  14. Nige

    Nige Senior Member

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    Correct. It's referred to as "J" in the attachment illustration.
     
  15. AUGUSTINO PALLADINO

    AUGUSTINO PALLADINO Member

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    I tried to pull the valve it's stuck in there good. Thinking of hooking a slide Hamer behind the spring, but I don't want to damage the valve or bore. Any ideas?
    My unit had two more valves on top compared to the illustration. I counted up from the bottom and came up with the stuck stick valve. Really appreciate your help.
    Augie
     
  16. Nige

    Nige Senior Member

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    Here's the complete valve parts list. I dunno if you can remove some hose connectors or whatever and get at the middle of the spool to find where the piece of whatever is causing it to stick is hiding.? Or could you get the other end cap off. Would that help at all.?
     

    Attached Files:

  17. Nige

    Nige Senior Member

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    Here's the D&A for the Control Valve. Maybe that might help. It shows a bit more of the internal parts of the valve.
     

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  18. Bluox

    Bluox Senior Member

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    If you can get the spring off the valve you will be able to push it in a bit and rotate the spool, some times this allows the stuck piece to come off the spool.
    If that works you should be able to fish out the piece.
    Good luck
    Bob