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The JLG 40F Boom Lift Dilemma

Discussion in 'Other Construction/Demolition Equipment' started by od1, Sep 13, 2009.

  1. OFF

    OFF Senior Member

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    Welcome Kbitt.
    The holding valve for the boom lift cylinder is a rectangular aluminium block bolted to the hydraulic piping on front of the boom lift cylinder. They do go bad sometimes. JLG part number 4640265

    The other possibility is a leaking manual decent valve. Make sure all 3 valves are tightly shut.
     
  2. Kbitt105

    Kbitt105 New Member

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    So is a holding valve the same as a counterbalance valve then? If so could I pull the return line back to the valve off and see if I get fluid from there? would that be an accurate way to diagnose if it is the counter balance valve? I am speculative of the manual descent falls. It is an older machine that set for quite a while. I used it quite a bit over the summer. Had the lift cylinder rebuild at the end of summer. Had no problems for a while after and then it slowly started leaking off.
     
  3. OFF

    OFF Senior Member

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    yes, same as counter balance. How fast is the boom dropping? Were the manual decent valves used/disturbed at all over the summer?
     
  4. maple2

    maple2 Member

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    I will hire you today! My 40f worked fine last fall when parked. Tried to get it going today. The drive, lift, swing will not work from the ground control or basket control. Is this more apt to be an electrical problem or hydraulic? If its electric would it be the wiring in the basket?
    Thanks for any help!!!
     
  5. OFF

    OFF Senior Member

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    More than likely, it's the solenoid for the dump valve on the proportional valve body. There's a cross member behind the engine, on the underside of that cross member are about three silver 12 volt solenoids. One for the dump valve, one for the horn, and the other for aux power. Might be four of them down there. Horrible spot. Take a good jumper wire/test lead and test each solenoid by connecting the large terminals of each solenoid together. One will blow the horn, etc. One should make your drive/lift/swing function.
    solenoid.jpg
    Common stuff, available at pretty much any auto parts store
     
  6. maple2

    maple2 Member

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    OFF Once again you saved the day!! Put a jumper on the solenoid, and that was the problem! I will pick up another solenoid at the parts store. Looks like the standard 12 volt solenoid.
    I want to thank you again!
     
  7. OFF

    OFF Senior Member

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    Good to know it worked out. :)
     
  8. NdnKirk

    NdnKirk Member

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    Just acquired a '79 JLG 40F, s/n 751138 everything seems to work. The kingpins or bushings are toast, I wonder if replacements are available? Steer tires are junk, new ones are on the way. There are over 90 trees on the ranch, a couple dead ones. I quit climbing 15 years ago.
     
  9. NdnKirk

    NdnKirk Member

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    Here's the new to me JLG 40F. JLG 40F Pic1.JPG
     
  10. NdnKirk

    NdnKirk Member

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    I wonder what switch is missing in the pic? JLG missing switch.JPG
     
  11. OFF

    OFF Senior Member

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    Welcome!

    the mercury switch seems to be hanging there. It should mount on the side of the rear boom cover. They break real easy. Nice looking machine for it's age. Hopefully all Racine valves. :D

    I'd be surprised if those king pins and bushings are still available. Know any machinists?
     
    Last edited: Jun 4, 2020
  12. OFF

    OFF Senior Member

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    I was wrong. Do a Google search for JLG #3420308 King Pin and #0960301 bushing, I see several places offering them for sale.

    The pin is a little rich at $240, but the bushings are only $12 something each.

    If you need a set of 40F manuals, message me with an email address I can send them to.
     
  13. NdnKirk

    NdnKirk Member

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    Thanks for the reply. That's the butt connector where a switch used to be. What's the mercury switch for, too much boom angle or lean? Probably takes four bushings? I really need manuals, not sure where to click to message?
     
  14. OFF

    OFF Senior Member

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    The mercury switch senses the boom angle, or at least it did in 1979. These days it's all done with micro-switches. The purpose was to cut out high engine RPM and high drive when ever the boom was above horizontal. Safety device.

    Yes, 4 bushings.
     
  15. NdnKirk

    NdnKirk Member

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    Should I replace the switch, are they available?
     
  16. OFF

    OFF Senior Member

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    I don't think they are available anymore. Society doesn't like liquid mercury used these days in anything. Pretty toxic stuff I guess.

    Not that a 40F is a fast machine, but you wouldn't want to be traveling 40ft up in the air in high drive & high engine. That's playing with fire. Let your fear guide you, remember to shut down the faster functions when up in the air. Being a lineman though, you probably have no fear.
    They were over-designed however. I remember them telling us you could blow a wheel off with dynamite, while fully extended, and they wouldn't tip.
     
  17. NdnKirk

    NdnKirk Member

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    I have fear, that's how I stayed safe for over forty years. I was thinking if I have a senior moment and forget to throttle down I might have a wild ride. Over design is a good thing, we count on it.
    Are Racine valves easily identified? New steer tires just arrived. Thanks for all the help.
     
  18. OFF

    OFF Senior Member

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    Here's what a 40F with Racine proportional valves looks like, marked as circle #1 in the picture.
    JLG 40F Racine pic.jpg

    this is Bertea valves. Note the big knobs.
    Bertea valves.jpg

    I have very little experience on 40F's with Bertea valves. Because they crapped out in the cold, JLG didn't ship Bertea machines to Canada. I only saw one or two Bertea machines, (maybe the same machine twice) so I never learned how they operate well enough to diagnose & repair over the internet.
     
  19. NdnKirk

    NdnKirk Member

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    Uh oh, I have Bertea. Probably can't get the joystick rubber bellows any more have you heard of any substitutes?
    I lived in Anchorage for 25 years, drove through Canada a number of times, eh. My son is in Fairbanks, he's moving down here next year but is keeping a cabin up there.
     
  20. NdnKirk

    NdnKirk Member

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    MSC Industrial Supply in AZ (928) 775-4918 has the JLG (Bertea) joysticks and parts for the joysticks; p/n B1 knob covers and p/n B6 boots are in stock and plentiful; not cheap but not crazy! They have other control parts too. I may have found a non-mercury replacement for the mercury switch. I haven't decided whether to order and try it yet. I'll let you know.
     
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