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  1. #1
    New Member
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    Jan 2011
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    Kubotas L3940 w/ FEL, B2910 w/ FEL & MMM;

    Default HST Power Loss on Kubota Grand L3940 HST+

    Hi and Thank you for an awesome site that has already helped me lots over the years just by reading... I'd like to ask advice with a problem that my dealer didn't address or repair when my tractor was recently serviced.
    My 2007 Grand L3940 HST+ with 380 hrs. on it always had tons of power for mowing/tilling, loader work, etc.; this summer, I had a local 21yr. old "help" me to mow, till and plant(80 machine hrs.) because I had to be out of town most of the spring/summer. This fall, when I got some precious "seat" time on her; I noticed that the hydro has a moderate whining noise now and I had to use Low HST Range with Low/Turtle Range on the Plus Lever just to maintain 2500rpm while brush hogging... I can't use High Range to roll down the lane or road like I used to either. The engine loses major RPM's whenever the HST pedal is pressed Fwd or Reverse(I think?)... (almost like the brake was on, but it's not) Hyd.Fluid appeared normal level/condition.

    I explained this to my servicing kubota Dealer and along with other parts/services, asked them to diagnose and remedy the loss of power issue, flush & change Hydraulic fluid/filters... an expensive($1300) service/parts bill later, absolutely no difference and the dealer said that they changed filter/fluid and thought that would solve the issue, but they didn't test drive it for power loss afterward other than loading it on my trailer... I should have tested it before picking it up... I'm working 6 hours away and can't conveniently trailer the tractor over several times, so I'm asking for help to get them going in the right direction when I take it back again...

    What specifically should I ask them to do to diagnose and remedy this issue? I've read of a hydraulic pressure check? There has been a substantial loss of power I'd have to relate to the HST based on my limited experience... Engine seems to start, come to normal temp and run fine otherwise.
    Thanks so much for any advice or direction based on your expertise or experience...

  2. #2
    Veteran Member kevinj's Avatar
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    West MI
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    BX-1860, L3940HSTC, B7500, Farmall M, Farmall 560D

    Default Re: HST Power Loss on Kubota Grand L3940 HST+

    How are the fuel filters???? Air filter????
    Kevin

    BX1860, mower, snowblower - B7500HST, FEL, Bush Hog - Grand L3940 HSTC, FEL, snowblower, 6' Landpride brush hog, 6' King Kutter tiller, Corn Pro 18+5 Fifth Wheel, 1950 Farmall M, Farmall 560D

  3. #3
    Veteran Member ccsial's Avatar
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    Jun 2005
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    1,569
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    NorthWest Illinois
    Tractor
    (Kuboto L3400) (Ford 1910 4WD w/FEL) (Deere X748SE) All bought new

    Default Re: HST Power Loss on Kubota Grand L3940 HST+

    Engine losing power (RPM's) sounds like contaminated fuel and/or filter.
    Kubota L3400-HST, Ford 1910-Gear FEL, John Deere X748SE

  4. #4
    Platinum Member Dead Horse's Avatar
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    Feb 2009
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    New Hampshire

    Default Re: HST Power Loss on Kubota Grand L3940 HST+

    or hydraulic system loading up..........

    I have seen this happen when a hose is not fully connected on a loader, or the stop has been removed at the top of the lift lever resulting in the lift piston constantly under load at full up.

    Sorry, no other ideas, except your dealer is an Idiot AND a thief.
    "We a two tractor family"

  5. #5
    Elite Member
    Join Date
    Sep 2008
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    3,388
    Location
    NE USA
    Tractor
    JD LA115, WH 244, Troy Built Horse 8 HP

    Default Re: HST Power Loss on Kubota Grand L3940 HST+

    Quote Originally Posted by RobK View Post
    Hi and Thank you for an awesome site that has already helped me lots over the years just by reading... I'd like to ask advice with a problem that my dealer didn't address or repair when my tractor was recently serviced.
    My 2007 Grand L3940 HST+ with 380 hrs. on it always had tons of power for mowing/tilling, loader work, etc.; this summer, I had a local 21yr. old "help" me to mow, till and plant(80 machine hrs.) because I had to be out of town most of the spring/summer. This fall, when I got some precious "seat" time on her; I noticed that the hydro has a moderate whining noise now and I had to use Low HST Range with Low/Turtle Range on the Plus Lever just to maintain 2500rpm while brush hogging... I can't use High Range to roll down the lane or road like I used to either. The engine loses major RPM's whenever the HST pedal is pressed Fwd or Reverse(I think?)... (almost like the brake was on, but it's not) Hyd.Fluid appeared normal level/condition.

    I explained this to my servicing kubota Dealer and along with other parts/services, asked them to diagnose and remedy the loss of power issue, flush & change Hydraulic fluid/filters... an expensive($1300) service/parts bill later, absolutely no difference and the dealer said that they changed filter/fluid and thought that would solve the issue, but they didn't test drive it for power loss afterward other than loading it on my trailer... I should have tested it before picking it up... I'm working 6 hours away and can't conveniently trailer the tractor over several times, so I'm asking for help to get them going in the right direction when I take it back again...

    What specifically should I ask them to do to diagnose and remedy this issue? I've read of a hydraulic pressure check? There has been a substantial loss of power I'd have to relate to the HST based on my limited experience... Engine seems to start, come to normal temp and run fine otherwise.
    Thanks so much for any advice or direction based on your expertise or experience...



    UGH!!!


    It could be simple or a bit of an issue

    If you have heavy black smoke while operating at speed the air filters are plugged.

    You could have water and algae in the fuel making it run erratic-highs, lows rather than with low power at all times; fuel filters are cheap but the condition of the fuel is always the issue as diesel fuel loves water and algae.

    The transmission turbine whinning indicates to ME that you are pumping air through the transmission control valves and cavitation is deadly for pumps and control valves.

    "I" myself would have pulled the pump and put it in a vice to check it for wear doing the following;


    After the pump is fully drained of oil-


    I would have taken a portion of clean oil and poured it into the inlet side of each pump section (if it has 2 sections)and when gear pumps are in good condition or new they will allow no more than a pencil lead thickness of oil to pass through the gear set or sets.

    If you have more oil than this draining through the pumps gear sets it is bad and needs to be changed.

    The transmission charge pump section will have a smaller gear set and will be running faster to deliver fluid to the trasmission control valve as it is much more demanding of fluid power and flow than the hydraulic system.


    Edit:


    If the engine is running up normally with no RPM issues as you stated with no water vapor
    comin from the exhaust-

    Have you checked the crankcase breather to see if it is clear of dead animals, wasp nests, nut shells, bedding materials like green grass, fiberglass, twine etc?

    If the breather is partially plugged it will reduce the engine performance considerably and can lead to blockage of the breather and a crankcase explosion.

    If they did not check this shame on them!!
    Last edited by leonz; 01-04-2011 at 01:23 PM.

  6. #6
    Super Member
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    central New York
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    all makes and models

    Default Re: HST Power Loss on Kubota Grand L3940 HST+

    I'd be in on the fuel filters!!!!! I don't know it's a hydro problem unless the brakes are locked on.

  7. #7
    New Member
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    Kubotas L3940 w/ FEL, B2910 w/ FEL & MMM;

    Default Re: HST Power Loss on Kubota Grand L3940 HST+

    Thank you all for your suggestions: Fuel Filter and Air Filter were both changed during the service and have always been changed or cleaned as needed. There is no unusual smoke and engine starts and runs normally. My tractor has always run and performed great at every task...until now. When sitting still, RPM's react normally when engaging the rear PTO to spin my 6' HD Brush Hog; it's when the HST pedal is pushed that the RPM's drop and the tractor has only 1/2 the power it did just a few months ago... I didn't use the FEL, but steering and non-load operation of FEL felt roughly "normal". kubota Dealer did a hydro flush/fluid/filter change and said that nothing unusual(filings/burnt matter) was present in fluid or filter. Previously I could run on my lanes or rural road in High with HST+ lever also up in high/rabbit with my 6'BH on 3pt with no effort whatsoever; now I've got to kick + lever down into low/turtle and even then the engine strains to maintain rpm's...
    I genuinely appreciate everyone's help and I will detail the final outcome for common good when it's resolved... any other suggestions? Thank you so much!

  8. #8
    Elite Member
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    NE USA
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    JD LA115, WH 244, Troy Built Horse 8 HP

    Default Re: HST Power Loss on Kubota Grand L3940 HST+

    If the inner safety element for the air filtration system
    (if it has one) was not thrown out it needs to be replaced
    and not cleaned-they are not ment to be cleaned.

    If it were me;

    1. I would first drain the existing fuel into a waste oil can through the suction line into a waste oil can or pan;
    a. change the inner safety element air cleaner if it has one.
    b. wash the inside of the fuel tank out with water and use a shop vac and small hose to suction all the water and debris out of the tank.

    look in the tank to see how clean it is and if there is still debris in the tank it needs more cleaning



    2. blow the suction line our with compressed air to be sure it is not clogged but it will not tell you if it is collapsed in normal use.

    3. replace the suction line with reinforced fuel tubing that will not collapse.


    4. pour "fresh" fuel into the tank and a can of www.seafoam.com

    5. bleed the air out of the fuel system.

    6. start the engine and run it at high idle in the parked position.

    7. let it run for an hour.



    If there are no symptoms of poor performance then it was the fuel tank and trash in the tank.

    If the poor performance continues change the fuel filters-dont clean them and let it run again for an hour at high idle in park.

    if symptoms persist you have bad fuel and it needs dual stage separation where in the installation of a racor fuel filter water separator like the 500FG3 is something you need to install to eliminate the fuel issues pre-injection pump.
    Last edited by leonz; 01-04-2011 at 02:34 PM.

  9. #9
    Gold Member Kubota 2350's Avatar
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    Aug 2009
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    Michigan
    Tractor
    JD 4310 / Kubota 2350

    Default Re: HST Power Loss on Kubota Grand L3940 HST+

    Keep us posted on this, I'm curious what's going on here.
    John



    Kubota 2350, MMM, Front Snowblower and Rear Blade

    JD 4310, FEL, Forks, Box Blade, Rear Blade and Rear Tiller

  10. #10
    Super Member
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    central New York
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    all makes and models

    Default Re: HST Power Loss on Kubota Grand L3940 HST+

    Please try the brake petals, we occasionally find that they are sticking because of lack of use on the hydro drive tractors and they feel like a big loss of power when you try and move the tractors.

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