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Case 1840 Hydrostatic Drive Issue Please HELP

Discussion in 'Skid Steers' started by Justice1840, Dec 20, 2018.

  1. Justice1840

    Justice1840 Active Member

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    I recently purchased this 1840 with the engine locked up (water in base pan)
    Machine sat more than it was used. Reading 249 hours. It was in good shape other than engine. Seller said that everything worked as it should when parked.
    When I got machine home i pulled cab, engine, tandem pumps, all hoses. I left motors, sprockets and chains in place. Properly capped motors and chain boxes and completely cleaned and repainted machine, rebuilt engine (4-390). everything appeared to be fine with tandem pump, so cleaned and painted and installed
    Got machine back together and runs great.
    Problem is that it will move forward and reverse, but with no power either way or either side. the warmer it gets the worse it gets until it will not move. it will not steer at all. has more power in reverse than forward, but nothing to be happy about. it will only move if close to wide open throttle. i have 300psi charge pressure. no pressure at either port on pump to motors. did the drain test and no oil coming from motor drains. i pulled all of the valves (circuit relief, bypass, charge pressure) and they appear to be fine, but cant be sure. i would like to mention that one of the post i read said that it should be hard to turn the input shaft. i recall (when tandem pump was out) that it was easy to turn input shaft. my next step is to remove tandem pump and go through it, but seems like it could be a simple fix and would hate to go through all of that if not necessary. i also replaced 90% of the hoses and cleaned them well before installing.
     
  2. alrman

    alrman Senior Member

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    Welcome to HEF @Justice1840
    Sounds heartbreaking......
    The charge pressure at 300psi is a little low, - is that reading at full RPM?
    Is that reading when cold? Does it change at operating temp?

    You also need to test the charge pressure again & see how much it drops when the drive is engaged under load - ie against the brakes (if they are working) slowly load the drive until the engine RPM begins to fall - the charge pressure should only drop about 20psi - any more & you need to do an autopsy on the hydrostatics.
     
  3. Justice1840

    Justice1840 Active Member

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    -yes it is heartbreaking. so close, i thought....
    -yes 300 plus or minus at full throttle
    -i will run again tomorrow to be sure what it does hot vs cold, not sure
    -i did test it under load with brakes engaged, it dropped, but again will check tomorrow to be sure how much
    -engine never drops at all. i can have both left and right side wide open against brake and no engine rpm drop
    Thanks for your reply
     
  4. Justice1840

    Justice1840 Active Member

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    So I checked charge pressure again this morning and got a different reading than before. I will explain the best I can.
    At initial start up with low RPM, I am getting 150psi constant. As I open the throttle pressure will go up. Lets say half throttle about 200psi. If I stay there for a minute it will start to fall, maybe 175psi. Than full throttle I'm around 250psi. Brakes engaged, moved drive control forward (right side) I loose about 5-10psi. The same in reverse. On the left side when I move control forward I get the same thing. When I move the left side in reverse, the gauge jumps up to around 300PSI and motor wines like low on oil. Now both controls in neutral wide open throttle the gauge is jumping rapidly from 5psi - 275psi. I throttle down to idle and have 5-10psi.
     
  5. Justice1840

    Justice1840 Active Member

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    My service manual says that I should have a minimum 300psi charge pressure. I understand that I am lower than 300psi. I am confused on why pressure is acting strange when left side reverse is engaged. Could a valve be stuck open and robbing pressure?
    Even though I am low on charge pressure shouldn't I still be getting some pressure to motors? When I put 5000psi gauge to A and B motor ports the gauge is hardly moving off of zero. If I cap off the hoses going to motors I get no rpm drop from engine. Nothing changes
     
  6. alrman

    alrman Senior Member

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    It does seem to be very peculiar....

    Can you explain why the engine was "locked up", ie -"water in base pan".
    Was water in the hydraulic tank as well??

    It seems there is a problem with the servo pistons binding & not allowing high pressure oil from the main pumps??
     
  7. Justice1840

    Justice1840 Active Member

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    There farm was flooded and supposedly water came up just over oil pan. When oil pan was removed you could actually see the water line. My guess was oil pan was leaking. It had one main bearing stuck. There was no water in hydraulic system. Oil was clean.
    The servos being stuck sounds believable. I had that thought also. Can I check servos without removing the pumps? It seems from what I can tell that the swash plate holds servo in? I’m not sure. I’m new to this
    I added a shim to the charge pressure check valve, just to see if pressure would rise. Little to no change
    I also checked case drain pressure today from pump, 10psi
     
  8. rondig

    rondig Senior Member

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    Are u getting proper suction for charge pump?
     
  9. Justice1840

    Justice1840 Active Member

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    I’m not sure about getting proper suction for charge pump.
    Can you explain how to check this?
     
  10. jacobd

    jacobd Well-Known Member

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    That is a strange issue. You've probably already checked all the simple stuff but just the same make sure the reservoir is full of the proper fluid (10w30 motor oil I believe) and the filter is good.
    I agree it sounds like the servos aren't stroking for some reason. You can check the pressure on the servo pistons by attaching gauges to the large ports on each servo end plate. In neutral the pressure difference should be zero and it should increase from there depending on load and how far the control is stroked. I believe you can also remove the end plates to visually inspect the servo housings.
    This may be of some help if you haven't seen it already. http://files.danfoss.com/documents/11026743.pdf
     
  11. alrman

    alrman Senior Member

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    Short of visually inspecting for any obstruction that may have been left in place during assembly - ie plastic cap, rag - I'm not sure either...
     
  12. Justice1840

    Justice1840 Active Member

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    Ok. I will try to put a gauge on servo caps and see what happens
     
  13. Justice1840

    Justice1840 Active Member

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    So I checked pressures on left pump servo. I’m not 100percent sure what the pressure is supposed to be, but I’m sure it’s not supposed to be what I’m getting.

    Reverse side of left servo I am getting around zero pressure in neutral. Gradually goes up as I move lever. Wide open I’m getting around 300psi

    Left servo forward side
    I’m getting around 250psi in neutral.
    I’m getting no change when lever is moved forward. If I move lever in reverse pressure goes to nearly zero

    ??????
     
  14. alrman

    alrman Senior Member

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    There is something very strange there....
    Technically, the LHS machine should be trying to drive forward while in neutral & it's not?

    Can you really believe the previous owners statement that "everything worked fine when we parked it up".......

    Was there any evidence the pumps have/have not been tampered with before you pulled it apart?

    I would be pulling the pumps & taking them to someone who really knows how they are supposed to work.
     
  15. Justice1840

    Justice1840 Active Member

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    Yea I agree, the machine should be moving in “neutral” and it’s not. However it does move forward when I move lever forward. Very strange. I’m wondering if one of the o-rings on servo is torn and allowing pressure? Not sure if it would do this or not.

    I know the people that I bought it from and don’t believe that they would have lied to me, but can’t be sure on that either.

    I didn’t see any evidence that it had been worked on before.

    I decided to remove the pumps today. Just got them out. Will attempt to pull apart tomorrow and hopefully see the obvious. My biggest fear is putting it back in and it doing the same thing. Was hoping to find the issue before pulling it out

    Thanks for all of the reply’s. I will keep you posted on what I find
     
    alrman likes this.
  16. Justice1840

    Justice1840 Active Member

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    Got the pumps disassembled today. Very clean inside, no metal shavings or debris that I could see.

    The servos appear to be ok as far as o-rings go and no scoring. They turn, but cannot move them side to side. Is this normal?

    I have quite a bit of scoring on both valve plates and also on cylinder block and piston faces. I will try to post pictures.

    Other than that I don’t see any obvious issues. Would these things cause my issue?

    How much can I take off of valve plates, cylinder blocks, and pistons without replacing? Or should I just replace?
     
  17. Justice1840

    Justice1840 Active Member

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  18. alrman

    alrman Senior Member

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    Well, that sheds some light on the issue!
    I don't consider myself an expert on these as I sublet these rebuilds to Sunstrand specialists for warranty reasons. However I have seen inside many of them.
    Yes, I believe this is your problem.
    I would think the servo pistons (without swash plates attached) should slide without too much force required to move them.
    The shop I use, has a lapping machine to polish those mating surfaces.
    Your end plates look like throw aways.
    The slippers look like they may clean up.
    How does the charge pump look?

    I hate to break it to you, but the drive motors will look the same.........
     
    Coy Lancaster likes this.
  19. Justice1840

    Justice1840 Active Member

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  20. Justice1840

    Justice1840 Active Member

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