1. Thank you for visiting HeavyEquipmentForums.com! Our objective is to provide industry professionals a place to gather to exchange questions, answers and ideas. We welcome you to register using the "Register" icon at the top of the page. We'd appreciate any help you can offer in spreading the word of our new site. The more members that join, the bigger resource for all to enjoy. Thank you!
  2. ALL NEW MEMBERS READ THIS FIRST!! Thank you for joining Heavy Equipment Forums! If you are new to forums we communicate with "Threads", please search our threads to see if your topic may have already been answered and if not then click "Post New Thread" in the appropriate forum. This will allow all of our members to see your question and give you the best chance to be answered. After you've made a number of posts you will graduate to Full Member status where you'll see a few more privileges. Following these guidelines will help make this the best resource for heavy equipment on the net. Thanks for joining us and I hope you enjoy your stay!!

why does my jlg 450a main boom settles

Discussion in 'Forklifts/Telehandlers' started by donald thompson, Jun 9, 2020.

  1. donald thompson

    donald thompson Member

    Joined:
    Jun 8, 2020
    Messages:
    7
    Location:
    iowa
    1 have a 1999 JLG 450A, #0300041500, dual fuel lift. the upper/main boom settles about 1.5 feet in 5 to 7 minutes. slower if the lift is shutoff and no one is in the basket, and a bit faster if the boom is extended all the way out.
     
  2. skata

    skata Senior Member

    Joined:
    May 10, 2007
    Messages:
    769
    Location:
    midwest
    Does it settle and stop? Or go all the way down?
     
  3. donald thompson

    donald thompson Member

    Joined:
    Jun 8, 2020
    Messages:
    7
    Location:
    iowa
    it will go all the way down
     
  4. skata

    skata Senior Member

    Joined:
    May 10, 2007
    Messages:
    769
    Location:
    midwest
    It's either worn seals inside the cylinder, or something wrong with the lock valve on the cylinder, that's the valve block mounted on cylinder that prevents the cylinder from moving in case of hose burst.
     
  5. Paul Council

    Paul Council Senior Member

    Joined:
    Oct 12, 2018
    Messages:
    380
    Location:
    Somewhere
    Leaning towards the holding valve on the boom cylinder.
     
    mg2361 likes this.
  6. donald thompson

    donald thompson Member

    Joined:
    Jun 8, 2020
    Messages:
    7
    Location:
    iowa
    if my memory is right i think we replace the seals on that cylinder about a year ago and the seals on the holding valve. that does not mean i did it right
     
  7. donald thompson

    donald thompson Member

    Joined:
    Jun 8, 2020
    Messages:
    7
    Location:
    iowa
    more info maybe? when the lower/mid booms are lower, it bounces. if i press the boom retract switch it stops the bouncing, even if the boom is not extended. release the switch after 2-3 sec and everything works fine until i do it again.
     
  8. Txhayseed

    Txhayseed Well-Known Member

    Joined:
    Dec 23, 2019
    Messages:
    87
    Location:
    Texas
    I would check the counter balance valves.
     
  9. 92U 3406

    92U 3406 Senior Member

    Joined:
    Jan 3, 2017
    Messages:
    1,482
    Occupation:
    Professional Wrench Spinner
    Location:
    Canuckistan
    2nd the counterbalance valves. Replaced many of those due to drift or leakage.
     
    Paul Council likes this.
  10. donald thompson

    donald thompson Member

    Joined:
    Jun 8, 2020
    Messages:
    7
    Location:
    iowa
    counterbalance valves, holding valve, lock valve, these are all the same valve right? in the block on the cylinder?
     
  11. Vetech63

    Vetech63 Senior Member

    Joined:
    Aug 10, 2016
    Messages:
    2,294
    Location:
    Oklahoma
    Correct. Different manufacturers call them different names but they are the same thing.
     
  12. donald thompson

    donald thompson Member

    Joined:
    Jun 8, 2020
    Messages:
    7
    Location:
    iowa
    thank you all. i guess i'll order a new valve and see if that fixes it
     
  13. donald thompson

    donald thompson Member

    Joined:
    Jun 8, 2020
    Messages:
    7
    Location:
    iowa
    replaced the holding valve and it appears to have worked. thanks to everyone