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  1. #1
    New Member
    Join Date
    Jun 2011
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    5
    Tractor
    Kubota B1750 hst

    Default Is my box blade too heavy for my tractor and damaging the hydraulics?

    I recently put a Land Pride 54inch 420lb box blade on my kubota B1750 4wd hst tractor. The manual said the weight limit for the rear lift arms are
    380lbs so I'm over by 40lbs. I used the box blade to grade my gravel driveway with no problems. When I used it with the shanks down to plow up my small garden (very soft soil) I had no problems except once the box filled up partially and I tried to raise the box blade and it refused to budge. I
    backed up a bit so the shanks were not biting into the dirt and that freed up the box.

    When I got the tractor back in the barn, lowered the box
    blade and shut off the engine I heard what sounded like escaping air and dripping. Hydraulic fluid was coming out from the area just above the pto
    spindle where the top lift arm gets its hydraulic power from. Aprox. 3 ounces of fluid came out before the drip stopped.
    I restarted the engine, raised
    and lowered the box blade, shut the engin., No more fluid came out at that time. I checked the hydraulic fluid level and it was in range on the
    dipstick.

    I was wondering if anyone experienced in these matters can advise me as to how serious this might be and what I should do to prevent any damage to
    the tractor. Might I have damaged a gasket? I hope I don't have to get rid of the box blade due to its being 40 pounds overweight.

    Thanks for any advise!

    Paul in Massachusetts

  2. #2
    Elite Member
    Join Date
    Sep 2003
    Posts
    4,144
    Location
    New Brunswick, Canada
    Tractor
    Kubota L5030 HSTC, MF 5455

    Default Re: Is my box blade too heavy for my tractor and damaging the hydraulics?

    The weight of the box is fine, trying to pick it up when box is full might exceed the lift capacity by a whole lot, ie it might need 1000 lbs lift to pick it up, but it should just make your hydraulics bypass.

    Not sure where the oil came from, on your tractor the lift piston should be enclosed below the seat area and the oil piped internally for the lift. If you have a loader, the block for that would have some fittings in the area to send oil to the loader then back to the internal passage for the hitch and you may just have had the pressure in the hitch circuit higher than ever before allowing you to detect a leak.

  3. #3
    Super Star Member J_J's Avatar
    Join Date
    Sep 2003
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    17,339
    Location
    JACKSONVILLE, FL
    Tractor
    Power-Trac 1445, KUBOTA B-9200HST

    Default Re: Is my box blade too heavy for my tractor and damaging the hydraulics?

    The forces of your tractor could apply more force than the cyl can take.

    If you had the 3pt in neutral, the 3pt valve would shut off all flow to the 3pt cyl.

    If you then tried to lift an immovable object, the force could suck in air at the cyl rod seal. It would seem like the air and fluid would flow out the valve in the down mode.

    You could install an external relief for the cyl to protect it.
    J.J.

    When I works, I works hard. When I sits and thinks, I goes to sleep.

    Git er done.

  4. #4
    Super Star Member J_J's Avatar
    Join Date
    Sep 2003
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    17,339
    Location
    JACKSONVILLE, FL
    Tractor
    Power-Trac 1445, KUBOTA B-9200HST

    Default Re: Is my box blade too heavy for my tractor and damaging the hydraulics?

    sandpipe,

    Have you checked the relief pressure on the 3pt valve. First, you need to know the pump max pressure or set the 3pt relief the same as the FEL valve.

    Yes, you can blow out the seals by over pressure, or put a bulge in the cyl tube .
    J.J.

    When I works, I works hard. When I sits and thinks, I goes to sleep.

    Git er done.

  5. #5
    Elite Member
    Join Date
    Jan 2010
    Posts
    2,628
    Location
    Northern, IL
    Tractor
    Branson 2400H

    Default Re: Is my box blade too heavy for my tractor and damaging the hydraulics?

    Quote Originally Posted by J_J View Post
    The forces of your tractor could apply more force than the cyl can take.

    If you had the 3pt in neutral, the 3pt valve would shut off all flow to the 3pt cyl.

    If you then tried to lift an immovable object, the force could suck in air at the cyl rod seal. It would seem like the air and fluid would flow out the valve in the down mode.

    You could install an external relief for the cyl to protect it.
    JJ,
    The only way you would increase the force on the 3PH is by trying to pull the arms down which would have a tendency to lift the front end. I guess I am at a loss on how a SCUT would over power the 3PH. Based on what I am reading I would expect to get more pressure spikes and or potential damage by driving down a rough road with the box blade bouncing on the arms Vs doing ground engaging work.

    Roy
    Artificial Intelligence will never overcome natural stupidity.

    Branson 2400H MMM & FEL

    JD 112

    BX1850 gone but not forgotten

  6. #6
    Super Star Member J_J's Avatar
    Join Date
    Sep 2003
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    17,339
    Location
    JACKSONVILLE, FL
    Tractor
    Power-Trac 1445, KUBOTA B-9200HST

    Default Re: Is my box blade too heavy for my tractor and damaging the hydraulics?

    I was thinking the fwd momentum at a fast speed, and hooking on something. Although there is a safety relief in the 3pt, no one ever speaks of it.

    About the same type of force as running the bucket into a pile of dirt with the weight of the tractor behind it. You might be able to generate much more force than the cyl can take. Hyd spikes, etc.

    Just thinking.
    J.J.

    When I works, I works hard. When I sits and thinks, I goes to sleep.

    Git er done.

  7. #7
    Elite Member
    Join Date
    Sep 2003
    Posts
    4,144
    Location
    New Brunswick, Canada
    Tractor
    Kubota L5030 HSTC, MF 5455

    Default Re: Is my box blade too heavy for my tractor and damaging the hydraulics?

    The 3 point does not always have a dedicated relief like the loader circuit. Not sure about this model.

  8. #8
    New Member
    Join Date
    Jun 2011
    Posts
    5
    Tractor
    Kubota B1750 hst

    Default Re: Is my box blade too heavy for my tractor and damaging the hydraulics?

    Thanks all for taking the time to try and solve my tractor problem.

    JJ: If you then tried to lift an immovable object, the force could suck in air at the cyl rod seal. It would seem like the air and fluid would flow out the valve in the down mode.

    >>You could install an external relief for the cyl to protect it.


    Maybe air was sucked in and then expelled with some fluid when I lowered the blade in the barn. Would installing an external relief valve prevent damage and is it a big deal to install? Also, might I need to bleed air out of the system?

    I still am wondering if i did any damage. In the next couple of days when there is a break from the rain I could go back out and retest the tractor to see if I created a chronic problem or if this wasn't just a one time event due to overloading the box blade. I'd like to resolve this asap since I will be needing the tractor to deal with snow in the not too distant future. (Wish I was going to Florida instead!)

    Does this make any sense or would a different procedure be better? I have very limited tractor experience so any advice is much appreciated!

  9. #9
    Veteran Member
    Join Date
    Jul 2010
    Posts
    1,311

    Default Re: Is my box blade too heavy for my tractor and damaging the hydraulics?

    After it has set for a few hours, check the fluid level. Does the area where it leaked some out have a vent? Could it be the vent was plugged and then let go?
    2007 Kubota L3130, LA723 FEL
    Land Pride FDR1672 rear finish mower, Frontier RB1172, Koyker KB60 BH
    Pallet forks, Golf cart canopy bolted to ROPS, 9" & 12" PHD

  10. #10
    Super Star Member J_J's Avatar
    Join Date
    Sep 2003
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    17,339
    Location
    JACKSONVILLE, FL
    Tractor
    Power-Trac 1445, KUBOTA B-9200HST

    Default Re: Is my box blade too heavy for my tractor and damaging the hydraulics?

    Just about every tractor that has a 3pt system would have a 3pt relief or a pump relief, but it is most common to put the relief in the 3pt area. The tractor may or may not ever have a loader installed.

    If you have a hyd gage installed in the hyd system, when you raise the 3pt to max up, the relief valve will activate and screech. Look at the gage to see the relief pressure.

    If you raise the 3pt and do hear the screech, that means that the pressure is at a level set by whoever. Most relief valves are set equal to the loader valve if installed.

    The relief should be about 50 to100 psi below the max pump pressure.

    You need to check the relief pressure anyway to see if the hyd system is working as advertised.
    J.J.

    When I works, I works hard. When I sits and thinks, I goes to sleep.

    Git er done.

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