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JLG 40HT no reverse, other issues and repairs

Discussion in 'Other Construction/Demolition Equipment' started by slceso, Jan 31, 2021.

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  1. slceso

    slceso Member

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    Hi all,

    This is kind of long, but I tried to include a lot of detail I'm hoping there's a JLG wizard out there who can give me some pointers. Basically I need help figuring out how to get reverse working again, or how I can put this thing in "tow mode" so I can roll it back some and steer it in forward.

    This is an old machine, and I can't find a lot more about it than the 3 manuals available at JLG.[​IMG]
    [​IMG]

    I've had it less than a week and bought from a local individual, who bought from another local individual, who bought from an electrical contractor several years ago. It has about 4300 hours.

    Current issue I am trying to resolve is the reverse drive. When I took delivery, it would run in reverse, but was very sluggish. I drove it around and cycled everything, and when I ran it 2 days later, no reverse.

    Right now I have driven it into a spot where I can't steer into a turn (edge of driveway and a steep grade). I tried flipping the hubs to disengage the drives, but I think the brakes are staying on, so I couldn't tow it. I tried running the controls to release the brakes at the same time and still couldn't tow it (maybe because it is 18,000 lbs).

    Things I've done so far:
    -swapped PQ controllers (Swing and drive) both work in the other spot identically.
    -verified 12v from the basket controller to the solenoid (PQ controller to reverse, 12v at solenoid wire)
    -measured solenoid coil (6 or 17 or so ohms, I can't remember, but was almost identical to the 2 solenoids next to it that function ok)
    -pulled solenoid, bench tested with 12v good (takes 1/2 a second and armature full extends)
    -pulled valve cover off, looked at proportional valve while oil ran out. The engine and pump were off, so I'm not certain if those bits are working right
    -disconnected valve outlet and cycled reverse prop control. When I did this it didn't seem to change the oil flow coming out, which was just kind of a dribble. I did this in several stages because I expected it to blast out of there, but it just slowly oozed out.
    -this leads me to believe it is the spool or whatever you call the bits in the valve.
    [​IMG]


    Other details on the machine:
    Mine was "installed" in 1986 based on the inspection date stamped on the machine.
    It has these variants of components:
    -Wisconsin dual fuel engine (although it looks like some of the propane bits are missing on the intake).
    [​IMG]
    -3 stick proportional controls, no steering wheel, Vickers Proportional valves (I think) with original square solenoids that are obsolete. The Lift prop control was replaces with a toggle, and there is some hack job wiring to accomplish that in the control box
    [​IMG]
    -Racine Bang-Bang valves (I think)
    [​IMG]

    Other things inoperable:
    -aux hydraulic
    -2 speed drive maybe
    -high speed drive maybe
    -engine high/low (it runs the same rev all the time)
    -swing prop control (replaced with 3 position toggle)
    -busted basket rotate hoses
     
  2. slceso

    slceso Member

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    I can't edit my post and links to Imgur didn't work (maybe because I am new), so here is the post on Imgur
    https://imgur.com/a/P7rRWeG
     
  3. slceso

    slceso Member

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    I think my next step will be to swap the drive output hoses before tearing into the "working section" AKA 7006760 PXL_20210131_214922708.jpg
    vickers valve.jpg

    PXL_20210127_140324831.jpg
     
    Last edited: Jan 31, 2021
  4. slceso

    slceso Member

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    Replaced 3 of the 4 hoses for the platform level and rotate. The 4th goes to the platform level cylinder inside the boom and I didn't know how I was going to get to that one (also I was afraid to have my hands chopped off when I pulled the line off of the cylinder and if it shifted). Looks like someone had modified one in the past and and added an additional fitting outside of the "choppin' hole." Because I am smart, I didn't mark the hose connections and it took 2 tries to get them on the right supply lines so that the platform didn't do random mechanical bull things when I operated it.

    For the reverse drive issue, swapped the hoses coming out of the proportional valve block. So now when I ran the control in forward, it should've sent flow to the reverse ports on the final drives. When this sequence happens, forward or reverse, the "dump valve" opens somewhere, and also oil is ported to the brake pistons on the drive wheels to release the brakes. It was wanting to reverse, but it was like the brakes wouldn't release. So I flipped the hub plates again and it seems like if the left drive was flipped, no power would go to the right drive (kind of like limited slip, but there is no differential, so it doesn't make sense to me. things were starting to also look like there was a problem with the right final drive or brake.
    valve block.jpg

    Next, I looked in the hydraulic filter housing, and what do ya know, there was no element, so clogged filter was definitely not the problem. I didn't really suspect that since all the other rams and swing work fine. I did note, though, that tank level was low in the sight glass, so I added about 4 gallons of VG68 (last guy used SAE-20, so they are supposed to be same weight) and gave it another go. This time I kept running it in reverse (control forward since I swapped the hoses) and after a minute the right drive seemed to free up (or re-engage from the hub disengage plate) and I was in business and able to drive her in reverse back to her designated parking spot.

    So it seems my problem is mostly in that proportional valve block. I bought a replacement prop controller 1600094 just to be sure and tested the swing and drive with that and it works the same as with the original controls. Next I guess I'll start taking the prop valves apart and see what I see.

    Also, can anyone tell me the function of the "Dual Overcenter Valve"? I think this is on the lower half in the "axle" area. It's downstream of the rotary coupling, and I don't think there are any electrics on it.

    Cheers!
    hydraulic drive lines.jpg

    dual overcenter valve maybe.jpg
     
  5. OFF

    OFF Senior Member

    Joined:
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    HD Mechanic
    Location:
    Alberta, Canada
    I've never seen a 40HT, so I kinda had this thread on ignore. Just looked at it for the first time. :oops:

    When you turned the plates over on your drives hubs, it disengages both drive motors and the brakes. You should have been able to tow it.

    What I would suggest you do for quick troubleshooting, is swap the two drive hoses around and see if your problem changes to forward from reverse. (drive function will be backwards of course) This will tell you if it's a controller/wiring/valve problem or something further downstream as you suspect.
     
    slceso likes this.
  6. slceso

    slceso Member

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    Hi Off,

    I did that today and it did change from not driving reverse to not driving forward, so I think it is an issue with the valve block in the first pic of my last post. I'll swap them back to normal so I can at least drive forward and try not to drive into a corner again.
     
  7. OFF

    OFF Senior Member

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    What you proved with the hose swapping is that there is nothing wrong from the proportional valve bank, to the wheels.
    Your problem is likely before or at the proportional valve.
    Have you checked drive voltage leaving the controller? At the terminal strip in the basket? At the terminal strip in the main control box? right at the valve? That would be my next step.
     
  8. slceso

    slceso Member

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    Hi,
    Yeah I put a meter on the leads to the coil and verified 12V when I tell it to reverse. I pulled the coil and actuated it on the bench, and measured it approximately same OHM as the coils next to it, so I think it is in the prop valve. I have zero experience with rebuilding a valve like that, but with most things I have to fix, taking it apart, cleaning it, and putting it back together fixes a lot of issues. might be a stuck ball check or something binding the servo or spool I guess. I just bought this in working shape to do a few jobs, so it is a disappointment that I only got about 30 minutes out of it before reverse quit on me. I wasn't looking for a fixer upper necessarily, but that's the way she goes.

    Thanks!
     
  9. OFF

    OFF Senior Member

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    Are you able to swap the two drive coils without disconnecting the wires?
     
  10. slceso

    slceso Member

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    Finally had a nice day and was able to get back to this. Wouldn't you know, I swapped the reverse solenoid with one of the lift solenoids and BAM, both forward and reverse works and the lift-lower now does not.

    It really confuses me because I pulled the suspect solenoid out and bench tested it with a 12V source and it actuates. Regardless, I don't have to go into the valve block so I am happy. Now I just have to find the obsolete solenoid replacements (I have square coils, no longer available, replaced by 7009360, 7009315). if anyone knows anything about that, I'd love to know more.
    2021-02-23_19-22-57.jpg

    2021-02-23_19-23-56.jpg

    Also, she does not like soft ground, so I had to use a dually F350 to tug on her while one of the kids drove the lift. 65% of the time, it works every time.

    PXL_20210223_212538189.jpg
     
    OFF likes this.
  11. slceso

    slceso Member

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    just went and messed with it some more. ohmed at 6 ohms. put a meter on the coil lead and could read 13 VDC. put meter inline to measure amp draw and got no amps. reconnected, now it works. ghost in the machine I guess. Also, I found my serial number: 0308609993

    for posterity, more part numbers I came up with:
    Got off the phone with JLG, and got some equivalent Vickers Part numbers:
    689610 Solenoid Coil [7009315 (coil and frame, round) has been superseded by Item 7020361 (KIT, COIL 12V FLYING LEAD), OBSOLETE]

    7009360 (Adaptor Kit, OBSOLETE) contained the following Vickers part numbers:
    686035 core tube (JLG 7009316, available, $302)
    680914 nut, retaining (JLG 7009317, OBSOLETE)
    924070 adapter plate (OBSOLETE)
    513771 pin (JLG 7009319, available, $15)