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!?! Kubota RTV 900 sudden lag in acceleration

Post in 'The Gear' started by pybyr, Aug 12, 2012.

  1. pybyr

    pybyr Minister of Fire

    Joined:
    Jun 3, 2008
    Messages:
    2,301
    Loc:
    Adamant, VT 05640
    I am fortunate in the extreme to have access to/ use of a Kubota RTV 900 for purposes of getting my firewood from the woods to my stacking location (a modest distance mostly through local woods and short backroad); I don't own it but am allowed to use it and in return do everything I can to actively maintain it/ use it with reasonable care.

    It's probably 3-4 years old with about 350 hours on it

    Today, for the first time ever, I am noticing that when I step on the throttle (which I always try to do gradually) there is a lag time or "wind up" that seems to need to take place before it moves forward with full "gusto." The diesel engine revs up with full promptness, it's as if there is something else that has to catch up... if it had a torque converter, I would be concerned about that, but to my knowledge,although it is hydrostatic, it does not have a torque converter.

    I first noticed it with a load in/ on it, but am also detecting this unloaded. Never detected this before.

    Off to go read the manual and check all fluid levels- but wanted to ask for any experience/ suggestions/ wisdom/ insight here. I really need to keep getting my wood out of the woods, so down time is a worry, but I also don't want to do anything adverse to the machine.

    thanks!

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  2. MasterMech

    MasterMech Guest

    Has the unit been in for service recently? If not then perhaps the linkage controlling the trans needs to be adjusted (my thinking is someone may have adjusted the linkage if it went in for service) or it's time for a hydraulic service.
  3. pybyr

    pybyr Minister of Fire

    Joined:
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    Loc:
    Adamant, VT 05640
    Checked the fluids and they are all full and clear (other than crankcase of course, which looks like what it is, a diesel engine...)

    All the fluid/filter, etc. change services I do. It was in for shop service very late 2011 after the main shift R-L-M-H linkage bound up and stuck (under tension pulling a load at the time) and they supposedly gave it a very full going through. This is actually the first time I have used it for firewood hauling to any degree since then.

    Guess I should try to gain a better sense how much the throttle pedal linkage interacts with the transmission in addition to the engine throttle; maybe the shop changed something having to do with how the throttle pedal interacts with the transmission and maybe this is just a slightly-differently-calibratedly version of "normal"
  4. pybyr

    pybyr Minister of Fire

    Joined:
    Jun 3, 2008
    Messages:
    2,301
    Loc:
    Adamant, VT 05640
    Anyone happen to have any suggestions on how I could develop a better understanding of how the innards of the Kubota RTV 900 utility vehicle hydrostatic transmission operates internally so that I can get a better sense of how much or what I need to be concerned about?

    I've got lots of familiarity and hands-on experience with regular hydraulic pumps, valves, cylinders, and motors, and with basic automatic transmissions, but not with the specific innards of this beastie. Nor does the owners manual shed any light on what's inside or how it functions.

    I have no illusions that I ought to be the one actually digging into it (which I assume would require specialized tools and experience beyond what I could bring to it), but would like to gain better understanding of its inner operation so that I can know how much of a concern its current "response lag" is (i.e. if something is out of whack, will additional use be at risk of additional damage). Thanks!!
  5. MasterMech

    MasterMech Guest

    My guess is that when the dealer worked on the linkage, they set the trans to act less aggressively as per Kubota's recommendations. One of the primary flaws in the RTV900 (or any of the RTV's for that matter) was that if it was in 2WD and the vehicle was travelling downhill, the trans made more than enough braking force to skid the rear wheels creating a dangerous, out-of-control downhill slide.
  6. MasterMech

    MasterMech Guest

    I don't think you're going to hurt the trans the way it is. But if you and the owner are unhappy with it's performance, perhaps the dealer would be willing to undo whatever it is they did to make the trans operate less aggressively.
  7. Countryboymo

    Countryboymo Feeling the Heat

    Joined:
    Feb 24, 2010
    Messages:
    409
    Loc:
    W Central MO
    The spark arrester is too fine mesh and plugs up restricting the engine horribly. I know almost everyone around here removes it cause it is right at the end of the outlet pipe and easy to remove. The air filter sucks a lot of dirt if driven in dusty conditions cause it is in front of the rear wheel and needs to be watched also. These are the first two items to check that most do not think about. Diesel engines are not controlled by intake air and fuel like a gasoline engine and suck a lot more air at all RPM ranges than a comparable gas engine so keeping a closer eye on the air filter is even more important.

    If you are in an area where the sparky is needed it is easy to clean but I would look into other options that are larger online or at a muffler shop because that little screen on a diesel is horrible engineering when a diesel outputs a ton more air just like it sucks in.
    http://www.messicks.com/Articles/RTV900-Service.aspx

    I did read somewhere that the factory muffler is spark arresting but didn't meet the us forestry service standards so they stuffed a screen up in the exhaust to make them happy.

    the units run night and day better without the screen.

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