4120 Hydraulic Issue -- any 4X20 guys out there?
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    Exclamation 4120 Hydraulic Issue -- any 4X20 guys out there?

    Hello Forum,

    Thank all of you for the welcomes. I hope to not wear them out. 2006 4120 PowerReverser open station with 228 hours. Original new purchase... mostly used to finish mow church ball fields and uproot small trees. Ran fine when parked, then bucket began to buck and became sluggish. Changed the spin on filter, cleaned the sump screen, 10 gal of Low-Vis and it ran all functions for about 30 seconds. Inline steering filter was clean. Stopped moving, no bucket, no rockshaft, no PTO and steering is ~binding. Most info says fluid/filters will fix this problem. I did lift the front end to burp steering and prime the system. Normal hydraulic service interval is 400 hours. NO metal in the screen, just aged fluid.

    The real clue here is that the hose coupling at the pump manifold partially collapses upon starting the tractor. The 1- 1/2" pipe is clear, the sump is clean, if the filter was clogged the bypass would allow fluid to the pump -- it was free and pops off at 7 PSI resistance and JD parts provided me a replacement filter in case the first was defective.... same thing. Obviously, the pump is not defective since it is asking for more fluid -- evidenced by the collapsing coupling. I did add additional clamps to the hose, but if it was cavitation (sucking air), it would not collapse: it would whine. I know someone in here has heard of or encountered this phantom trouble... I did work the SCV and lift to exhaust all old fluid before change.

    Is it possible that the PTO relief valve could vent more fluid than the pump can provide, or am I a victim of airlock and heading the wrong direction? Anyone know of a step-wise bleeding system in this situation? I thought this was self priming and BTW, the case vent is open - no dirt dobbers... I appreciate any input as I am dead-in-the-water where it sits and desperately need before winter.

    Thanx in advance - FF

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    Captain Hook Kennyd's Avatar
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    The system should be self bleeding as you suggested, but you can try to turn the PTO on to help get things going if it's electrically operated-that trick works on the little compacts.

    Is it part #16 that is collapsing?
    Attached Thumbnails Attached Thumbnails Capture.JPG
    Kenny

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    Yes, Kenny,
    The hose coupling just below the pump manifold. It will close up as much as the two pipes will let it. There might be an 1" +/- between the two pipes and it will collapse to almost half the diameter. By all rights, it should only be the 2 filters, but it is venting off somewhere or not going somewhere. NO activity at the PTO and I am scared of burning the wet clutch without any pressure back there. That is why I keep thinking that it is dumping faster than the pump can supply. I have a replacement hose but it is just as supple as the one on there. I thought of pulling the manifold, changing the hose while there, and priming the the pipe and the pump and trying again. Someone mentioned that the hose should have a steel coil in it like a lower radiator hose but it does not. I have ordered a 5000 PSI gauge, but that is useless until I get pressure somewhere...
    Thx-FF
    BTW, I am Bob.
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    Captain Hook Kennyd's Avatar
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    Bob,
    My only other thought is the sump screen is in backwards blocking the flow...if thats even possible. I looked in JDParts but only saw the screw on filter-couldn't find a screen (or what typically looks like a screen anyway.
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    Kenny

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    MINICUP28's Avatar
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    What Changed Since It worked Last?

    I wonder if the NEW filter might be suspect? A collapsed hose on the suction side. If the filter were assembled incorrectly or there is something blocking it's inlet would cause the hose to collapse.
    The fact that they put a tell-tale viewing port there might make you think it's happened before a lot.
    Keep us posted on your progress.
    TIM
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    Captain Hook Kennyd's Avatar
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    Quote Originally Posted by MINICUP28 View Post
    I wonder if the NEW filter might be suspect? A collapsed hose on the suction side. If the filter were assembled incorrectly or there is something blocking it's inlet would cause the hose to collapse.
    The fact that they put a tell-tale viewing port there might make you think it's happened before a lot.
    Keep us posted on your progress.
    He wrote the he tried a second filter:

    ...it was free and pops off at 7 PSI resistance and JD parts provided me a replacement filter in case the first was defective...
    Kenny

    -John Deere 3720 Deluxe Cab TLB
    FEL, MMM, Artillian 42" Forks and Modular Grapple, I-Match, Ballast Box, and lots of other STUFF.
    -John Deere 455 w/60" MMM


    Bolt on Grab Hooks and other cool stuff are now for sale!!

    Visit our YouTube Channel

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    John Deere 3720 Deluxe Cab, 300cx FEL, 366 Front Blade, 59" Front Snowblower, Ballast Box
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    Zebrafive's Avatar
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    Quote Originally Posted by FrustratedFarmer View Post
    Yes, Kenny,
    The hose coupling just below the pump manifold. It will close up as much as the two pipes will let it. There might be an 1" +/- between the two pipes and it will collapse to almost half the diameter. By all rights, it should only be the 2 filters, but it is venting off somewhere or not going somewhere. NO activity at the PTO and I am scared of burning the wet clutch without any pressure back there. That is why I keep thinking that it is dumping faster than the pump can supply. I have a replacement hose but it is just as supple as the one on there. I thought of pulling the manifold, changing the hose while there, and priming the the pipe and the pump and trying again. Someone mentioned that the hose should have a steel coil in it like a lower radiator hose but it does not. I have ordered a 5000 PSI gauge, but that is useless until I get pressure somewhere...
    Thx-FF
    BTW, I am Bob.
    I would not worry about burning up the PTO clutch. It is "living" in oil, and slips until the piston receives hydraulic pressure to squeeze the drive and driven plates together to power the PTO shaft. If it does not get any pressure, it will act as if the PTO has not been engaged.
    J
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    Zebrafive's Avatar
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    I would be tempted to try with the sump strainer removed to rule it out.
    J
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    Thanks for the reply, Zebrafive,

    The screen (stainless mesh) was washed in diesel and blown dry.
    There was no metal - only a little gunk - didn't seem enough to
    clog the filter. The third filter (steering to PowerReverser) was
    clean. Remember 228 hours gentle use.

    Also, RE: Kennyd, the screen is symmetrical as seen in the
    attachment. There is a flange on each end-- one to the
    suction elbow and one to a blank (on my 4120) with a plug
    on the other side of the case which fits into a machined hole
    in the case. I assume this is for an additional aux attachment.
    It comes from the same filtered side.

    Lots of rain here the past days. Should clear tomorrow.

    -FF

    P.S. 30+ years in automotive automatic/standard transmissions,
    fuel injection, computer control... now retired medical. Someone
    must have had this same issue... I believe my technique solid.
    Attached Files Attached Files

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    Sorry, OOPs, looks like the .pdf didn't work.
    Here is the link to the pic of the screen:

    https://www.tractorbynet.com/forums/..._strainer-jpg?

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