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  1. #1
    Bronze Member
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    Nov 2008
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    Kerrville, TX
    Tractor
    2006 Kubota L39 TLB, Bobcat S160 Skid Steer

    Default L39 Hydraulic Shudder When Hot

    Well, south Texas is getting HOT. This weekend, after about 4 hours in 90+ temp (but the engine temp guage was normal) I noticed my L39 hydraulics started to shudder on the backhoe and FEL when I was making small - slow movements on the FEL or hoe. Normally, everything is smooth as silk. I noticed it last weekend too - but I thought it was just my imagination and being hot and tired after 4 to 5 hours seat time. But, this weekend after 4 hours of almost constant operation - the shudder was definately there.

    My L39 has almost 900 hrs and I've put the last 125 hrs on it. I bought it used from kubota dealer and he changed all filters a fluids at 775 hrs. I checked fluild level and it is at the top mark where it has been. No leaks on concrete floor at all. However, when I did check the fluid level later Saturday evening, I noticed a few very small (tiny) bubbles in the fluid - not foam - just several tiny bubbles on the dipstick. I didn't remember seeing them ever before??????

    Any ideas??

  2. #2
    Elite Member gwdixon's Avatar
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    2,617
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    Northern CA

    Default Re: L39 Hydraulic Shudder When Hot

    My L48 does exactly the same thing. After the hydraulic fluid gets hot the boom gets jumpy.

    I figured that it was because cheap hydraulic fluid was used at the last change (Traveler Premium from Tractor Supply). My thought that it thinned out too much when hot compared to UDT or true premium oil.

    There is 15 gallon store of New Holland Ambra in my shed just waiting until the opportunity comes for a change-out. Only 125 hours on the cheap oil.

    I'll be happy if someone comes up with a better answer.
    2009 Kubota M7040, R1s, LA1153 FEL, fork lift, 3 rear remotes, T&T
    2002 Kubota L48 TLB, 12", 18", 24" HD buckets
    2001 Kubota BX2200, Turf, LA211 FEL
    7.5' Howse 3PT disc, 88" Gearmore 4G4 box scraper, 4' box scraper, Gearmore GB85 blade, LandPride RCR2596 cutter, 6', 4' flail mowers, 6', 4' rototiller, 4' Bush Hog cutter, HD subsoiler, Bearcat 70554 chipper, Bush Hog PHD w/ 12", 6" augers, Ford 101 3-bottom plow, 8' land leveler, 6' rake, lots of misc.

  3. #3
    Veteran Member chim's Avatar
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    Apr 2002
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    1,881
    Location
    Lancaster County, PA
    Tractor
    Kubota L3200, Ford 1210

    Default Re: L39 Hydraulic Shudder When Hot

    Don't blame it on your choice of hydraulic oil. I used UDT and Super UDT in a tractor that did something like you're discussing.

    On the B7500 I had the steering would get a very noticeable "jerky" feel. It only happened while pushing it on the hotter days when using the 5' RFM in heavier grass. I blamed it on two things - The large heavy Landpride RFM and a smaller than ideal hydraulic cooler. I could make everything feel like normal by swinging by the garden hose and running cool water over the hydraulic cooler fins with the tractor idling for a few minutes.

  4. #4
    Platinum Member
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    Jun 2005
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    899
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    Central NH (God's Country)
    Tractor
    Kubota 1982 B7200 , L-39(2005) Kubota RTV 900 (2005) & Komatsu PC75UU2E(1997), Mahindra Max28XL Shuttle

    Default Re: L39 Hydraulic Shudder When Hot

    Quote Originally Posted by Jim Miller View Post
    Well, south Texas is getting HOT. This weekend, after about 4 hours in 90+ temp (but the engine temp guage was normal) I noticed my L39 hydraulics started to shudder on the backhoe and FEL when I was making small - slow movements on the FEL or hoe. Normally, everything is smooth as silk. I noticed it last weekend too - but I thought it was just my imagination and being hot and tired after 4 to 5 hours seat time. But, this weekend after 4 hours of almost constant operation - the shudder was definately there.

    My L39 has almost 900 hrs and I've put the last 125 hrs on it. I bought it used from kubota dealer and he changed all filters a fluids at 775 hrs. I checked fluild level and it is at the top mark where it has been. No leaks on concrete floor at all. However, when I did check the fluid level later Saturday evening, I noticed a few very small (tiny) bubbles in the fluid - not foam - just several tiny bubbles on the dipstick. I didn't remember seeing them ever before??????

    Any ideas??
    Air or a sticky relef valve maybe?

  5. #5
    Bronze Member
    Join Date
    Nov 2008
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    64
    Location
    Kerrville, TX
    Tractor
    2006 Kubota L39 TLB, Bobcat S160 Skid Steer

    Default Re: L39 Hydraulic Shudder When Hot

    OK - The next time I use the L39, before I get going, I'm going to be very careful to look for any noticable bubbles in the fluid on the dip stick. Then I'm going to do my work until I feed the shudder come back. When it does (and I believe it will) I'll check the fluid for bubbles again and then try the garden hose cool-down on the hydraulic cooler fins trick for a few minutes.

    I'll let you all know what I find.

  6. #6
    Bronze Member
    Join Date
    Nov 2008
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    64
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    Kerrville, TX
    Tractor
    2006 Kubota L39 TLB, Bobcat S160 Skid Steer

    Default Re: L39 Hydraulic Shudder When Hot

    I'm the OP and my last post about this was in June 2012. My L39 still has the "jerky" feel after running about an hour or more. The FEL, backhoe and clutch all feel jerky after an hour of operation. When I push in the clutch my foot feels a small roughness that wasn't there before. When I operate the FEL or hoe, all the operating motions just get jerky. This is hard to exactly describe but if you've been using the tractor and everything has been smooth and then you notice all the movements are not smooth anymore it gets your attention. When I'm trying to be very careful where I'm putting the hoe or trying to gently ease the FEL down to dump something it really gets more tricky than usual.

    I still have the tiny bubbles in the fluid and the fluid level is still at the full mark. When I first begin working, the tractor is very smooth and then it begins to have that studder or jerkyness.

    I don't think it's a sticking valve - but - it is definately heat related. No leaks at all.

    I'm open to any suggestions - including changing the hydro and filters. I just wanted to bring this back up to the forum to see if anyone might be able to help me.

    Thanks!

  7. #7
    Elite Member gwdixon's Avatar
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    Default Re: L39 Hydraulic Shudder When Hot

    Quote Originally Posted by Jim Miller View Post
    I'm the OP and my last post about this was in June 2012. My L39 still has the "jerky" feel after running about an hour or more. The FEL, backhoe and clutch all feel jerky after an hour of operation. When I push in the clutch my foot feels a small roughness that wasn't there before. When I operate the FEL or hoe, all the operating motions just get jerky. This is hard to exactly describe but if you've been using the tractor and everything has been smooth and then you notice all the movements are not smooth anymore it gets your attention. When I'm trying to be very careful where I'm putting the hoe or trying to gently ease the FEL down to dump something it really gets more tricky than usual.

    I still have the tiny bubbles in the fluid and the fluid level is still at the full mark. When I first begin working, the tractor is very smooth and then it begins to have that studder or jerkyness.

    I don't think it's a sticking valve - but - it is definately heat related. No leaks at all.

    I'm open to any suggestions - including changing the hydro and filters. I just wanted to bring this back up to the forum to see if anyone might be able to help me.

    Thanks!
    Since you have diagnosed the problem to be heat related (correctly I believe) then the only solution would be to make modifications to lower the heat of the hydraulic fluid. Did you diagnosis include manually feeling the cylinders to verify that they are hot? Harbor Freight and others sell non-contact thermometers that can help determine at what cylinder temperature functions start to fail.

    I have not heard of using a transmission fluid type of cooler on tractor hydraulics but one could make a fortune if something of that sort could be developed. I know that I'd buy one for my L48.

    The other option is to deal with the hydraulic oil itself. Using an oil that has a higher viscosity may help as well as using some synthetics (Amsoil).

    This link is to an explanation of many of the aspects of hydraulic oil. It may help you in looking for a solution:

    Characteristics of a Good Hydraulic Fluid - Hydraulics 101 - HydraulicFacts

    Here is a quote (post #54 in this tread http://www.tractorbynet.com/forums/k...filters-6.html )

    So I just compared the specs of SUDT2 to AMSOIL. Because I believe my power steering problem is somehow related to the hydraulic fluid over-heating, the spec in which I'm most interested is the Viscosity @ 100 degees C, cSt. The SUDT2 is rated at 8.1. The AMSOIL is 9.8. Higher is better.
    2009 Kubota M7040, R1s, LA1153 FEL, fork lift, 3 rear remotes, T&T
    2002 Kubota L48 TLB, 12", 18", 24" HD buckets
    2001 Kubota BX2200, Turf, LA211 FEL
    7.5' Howse 3PT disc, 88" Gearmore 4G4 box scraper, 4' box scraper, Gearmore GB85 blade, LandPride RCR2596 cutter, 6', 4' flail mowers, 6', 4' rototiller, 4' Bush Hog cutter, HD subsoiler, Bearcat 70554 chipper, Bush Hog PHD w/ 12", 6" augers, Ford 101 3-bottom plow, 8' land leveler, 6' rake, lots of misc.

  8. #8
    Bronze Member
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    Nov 2008
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    64
    Location
    Kerrville, TX
    Tractor
    2006 Kubota L39 TLB, Bobcat S160 Skid Steer

    Default Re: L39 Hydraulic Shudder When Hot

    Does the L39 have a transmission cooler? I know I don't have a transmission temp guage. I've been thinking about borrowing my meat themometer to dip into the fluid fill port. Or would one of those temp guns be better. Once I find the temp that the hydro gets jerky - then what should I do. I'm just trying to think ahead after I find that the jerky movement starts at 157 degrees. I don't know what to do with that information.

    If the L39 has a cooler - then maybe its plugged up and not working correctly.

  9. #9
    Elite Member gwdixon's Avatar
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    Default Re: L39 Hydraulic Shudder When Hot

    The information from the heat gun could verify and isolate the problem. If the boom repeatedly becomes jerky at around 157+ degrees measured at a consistent point on the boom cylinder, then the diagnosis would be more certain. No concern about a sticking valve or the like.

    The air bubbles in the oil situation is an indicator that the hydraulic fluid you are using does not have adequate foam inhibitors to break up the bubbles (foam). Those bubbles can create problems.

    Foam results from air or other gases becoming entrained in the hydraulic fluid. Air enters a hydraulic system through the reservoir or through air leaks within the system.

    A hydraulic fluid under high pressure can contain a large volume of dissolved or dispersed air bubbles. When this fluid is depressurized, the air bubbles expand and produce foam. Because of its compressibility and poor lubricating properties, foam can seriously affect the operation and lubrication of machinery.

    Proper foam inhibitors modify the surface tension on air bubbles so they more easily break up.


    While the dealer may have changed the hydraulic fluid you can't be sure what he used or even that it was done. Hydraulic fluid stays quite clear over time. It does lose some of its additives and lubrication when old. The link I posted about the "Qualities of a Good Hydraulic Fluid" details many factors that may have lead to the problems you are experiencing.

    Now you have to decide if it is worth $400, or so, to change the hydraulic fluid to Amsoil and replace the hydraulic and transmission filters. Right now, you are trying to evaluate a problem without full knowledge of the parameters.

    As far as I know, none of the smaller kubota backhoes have a transmission cooler. That would indicate to me that Kubota engineers expect the quality of the fluid should adequately dissipate the heat build-up. In addition, quality fluid would be less likely to get hot and reduced viscosity resulting in lack of lubrication and functioning.

    In summary, change the oil and filters and don't go cheap.

  10. #10
    Platinum Member
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    Oct 2010
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    Location
    Northern, NJ
    Tractor
    Kubota L45

    Default Re: L39 Hydraulic Shudder When Hot

    My L39 had a hydraulic cooler on the front in front of the radiator. I found out the hard way when a little rubber hose broke and spewed fluid everywhere.

    ac

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