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  1. #1
    Bronze Member
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    Apr 2011
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    78
    Location
    Forest Ranch, CA
    Tractor
    Kubota L3540

    Default Backhoe cylinder problem? (w/ video)

    I think I have a problem with one cylinder on my kubota BH77 backhoe, but maybe it's working correctly and my expectations are wrong.

    Here's a short video I made yesterday to demonstrate the "problem":
    Kubota Backhoe BH77 Cylinder Problem? - YouTube

    What do you think? Is it working correctly or is there a problem?

    Should the cylinder compress that easily? Should a cylinder develop "slack" that allows the bucket to bounce?

    thanks for any and all input!

    -Jeff
    Kubota L3540 HST-3, LA724 Loader w/ 3rd function valve & quick attach bucket, BH77 Backhoe, 72" Box Blade, 84" Quick Attach FEL Snow Blade, 48" NAI Grapple
    Located 3200 feet elevation in the Sierra Nevada foothills of Northern California

  2. #2
    Platinum Member
    Join Date
    Apr 2010
    Posts
    975

    Default Re: Backhoe cylinder problem? (w/ video)

    It looks like you have a brand new hoe, yes?

    If so, you almost certainly have air in the cylinder. Fully extend the cylinder and HOLD the control to keep it extended for 5 full seconds. Then fully retract the cylinder and HOLD the control to keep it retracted for 5 full seconds. You should hear the air going past the pressure relief valve and should see foam in the fluid reservoir. You will need to check the fluid level, top it off and if there are bubbles in the fluid wait a bit for them to go away then repeat until the fluid level stays the same. I would do this with every cylinder.

    If it's NOT a new hoe and it was previously working correctly, then there are other things to look into.

  3. #3
    Bronze Member
    Join Date
    Apr 2011
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    78
    Location
    Forest Ranch, CA
    Tractor
    Kubota L3540

    Default Re: Backhoe cylinder problem? (w/ video)

    Quote Originally Posted by Ford tractor View Post
    It looks like you have a brand new hoe, yes?

    If so, you almost certainly have air in the cylinder.
    Thanks for the reply.

    The hoe is new-ish... it was new in July and now has 8-10 hours of digging on it. I have already done the "purge the air" procedure with no difference.

    The dealer has also worked on the backhoe twice already: the first problem was it would not hold it's position and would droop. He said the fix was "cleaned some assembly gunk out of the relief valve". Second problem was the dipperstick had no power and moved VERY slowly. He said the fix for that was "replaced a valve".

    The dealer has not responded to this last problem. So I'm hoping to learn as much about it as possible so I can "make my case" to him.

    -Jeff
    Kubota L3540 HST-3, LA724 Loader w/ 3rd function valve & quick attach bucket, BH77 Backhoe, 72" Box Blade, 84" Quick Attach FEL Snow Blade, 48" NAI Grapple
    Located 3200 feet elevation in the Sierra Nevada foothills of Northern California

  4. #4
    Gold Member jmanatee2's Avatar
    Join Date
    Feb 2011
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    298
    Location
    Southwest NH
    Tractor
    Kubota L39 TLB

    Default Re: Backhoe cylinder problem? (w/ video)

    if you pull on the dipper and bucket at the same time does it do the same thing?

    If it does I would think the piston is leaking.

    If not might be a control issue.
    2006 Kubota L39
    QA SSQA Pallet forks
    Wallenstein BX42s Wood Chipper
    King Kutter 72" Pro HD Box Blade
    King Kutter Box fram Disc 20-20
    HF 3 Pt Quick Hitch
    1979? John Deere 350B Dozer with 6 way blade

  5. #5
    Silver Member
    Join Date
    Aug 2009
    Posts
    179
    Location
    Port Orchard, WA
    Tractor
    Kubota L4310 GST;Case 580 CK (1968)

    Default Re: Backhoe cylinder problem? (w/ video)

    Definitely not right. I used the dipper and boom inconjunction with the curl cylinder and managed to bend the rod on the curl cylinder. In other words, when working properly, the dipper shoudl not collapse.

    This might be better on the hydraulics forum, but I suspect a control valve issue. The fuild is not bypassing the seals of the cylinder, it is being evacuated from the cylinder, hence the slack. Something is goofy.
    Cycle_Gator,
    Port Orchard, WA
    Kubota L4310 GST

  6. #6
    Gold Member jmanatee2's Avatar
    Join Date
    Feb 2011
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    298
    Location
    Southwest NH
    Tractor
    Kubota L39 TLB

    Default Re: Backhoe cylinder problem? (w/ video)

    The more I think about it, There must be air in the dipper cylinder. If there was fluid it wouldn't move like that when it comes off the stump.

    The bounce is caused by compressed air expanding.

    JMHO
    2006 Kubota L39
    QA SSQA Pallet forks
    Wallenstein BX42s Wood Chipper
    King Kutter 72" Pro HD Box Blade
    King Kutter Box fram Disc 20-20
    HF 3 Pt Quick Hitch
    1979? John Deere 350B Dozer with 6 way blade

  7. #7
    Platinum Member
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    Apr 2010
    Posts
    975

    Default Re: Backhoe cylinder problem? (w/ video)

    Quote Originally Posted by caspar3259 View Post
    Thanks for the reply.

    The hoe is new-ish... it was new in July and now has 8-10 hours of digging on it. I have already done the "purge the air" procedure with no difference.

    The dealer has also worked on the backhoe twice already: the first problem was it would not hold it's position and would droop. He said the fix was "cleaned some assembly gunk out of the relief valve". Second problem was the dipperstick had no power and moved VERY slowly. He said the fix for that was "replaced a valve".

    The dealer has not responded to this last problem. So I'm hoping to learn as much about it as possible so I can "make my case" to him.

    -Jeff

    Couple comments. Obviously the hoe has issues. Equally obviously, the dealers is about as incompetent as they come. You probably figured that out, but I thought you might like to hear it from someone else.

    Looking at the video it looked like the dipper stick cylinder "sprung back" when tension was removed. If it's fluid bypassing, that CAN'T happen, as in impossible. Fluid doesn't compress - air compresses. You still have air in the cylinder because the cylinder bounced back out. (unless the hose was swelling like 3x it's diameter....). Time to get "aggressive". Pull back that lever and hold it full back for 1 full minute with the engine at PTO RPM's. Use a watch. Then push it full forward for 1 full minute. You will be bypassing the fluid across the relief valve the whole time and the fluid will be heating up -- keep an eye on that. Actually, a hand. The fluid will get hot, that's ok as long as it stays under 300F. Normal operating temps are 140-180F. Short excursions to 200-250 are not an issue at all.

    I suspect that there are multiple issues.

    You REALLY need to spend 20-30 bucks and buy a pressure gauge that reads up to 3500 or so and the adapters to fit to the working ports of the hoe control valve. Check that you are actually reaching the operational spec pressure. Some systems set the pressure at the control valve, but some kubota's set it in a block on the tractor by changing shims. You can get them pretty cheap. IIRC they are like 150psi per mm. On new systems going 150-200 psi over spec is ok as the relief spring will quickly weaken and settle down that much -- then hold it there for a long while. You might have to take off a hose and bring it to a hydraulic shop to get the correct adapter - or else visit the dealer. But I don't have much faith that your dealer can find his butt with both hands...

    If you have a cylinder that is bypassing, you can test for that pretty easy (but not neatly!). Fully extend the cylinder, then REMOVE the hose from the cylinder on the retract side. Then with the hose still off, move the control to extend the cylinder. You will probably get a shot of fluid out as the cylinder moves a bit, then you should get just a few drips to a very minor dribble. That dribble will get worse over time as the cylinder and seals wear. Seals can hold in one direction and leak in the other, so you have to repeat with the cylinder retracted.

    If there is no air in the cylinder and the cylinder is not internally bypassing (and visually not externally from your vid), then the only place left is the control valve. If the relief valve is set correctly and not opening early (detected by a low gauge pressure) then there may be internal bypassing in the valve.

    Hope this helps.

  8. #8
    Super Star Member J_J's Avatar
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    Sep 2003
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    16,419
    Location
    JACKSONVILLE, FL
    Tractor
    Power-Trac 1445, KUBOTA B-9200HST

    Default Re: Backhoe cylinder problem? (w/ video)

    That cyl definitely is not working correctly. That cyl should be in hyd lock with the spool for that cyl in neutral. If it moves, there is air in the cyl, especially if the cyl rod extends after being pressed in.

    I agree with the air in cyl. Cycle the dipper cyl several times and see if it still does it. You could also put a gage in the cyl circuit and read the pressure.

    Check and see if you have air in all the cyl. Possible suction leak on the pump.
    Last edited by J_J; 09-15-2011 at 08:32 AM.
    J.J.

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

    Git er done.

  9. #9
    Bronze Member
    Join Date
    Apr 2011
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    78
    Location
    Forest Ranch, CA
    Tractor
    Kubota L3540

    Default Re: Backhoe cylinder problem? (w/ video)

    Thanks for all the suggestions and explanations. I'll try the "aggressive" air purge and see if that makes any difference. If the problem continues (or comes back later), I'll go back to the dealer and ask him to make it right.

    -Jeff
    Kubota L3540 HST-3, LA724 Loader w/ 3rd function valve & quick attach bucket, BH77 Backhoe, 72" Box Blade, 84" Quick Attach FEL Snow Blade, 48" NAI Grapple
    Located 3200 feet elevation in the Sierra Nevada foothills of Northern California

  10. #10
    Platinum Member
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    Apr 2010
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    975

    Default Re: Backhoe cylinder problem? (w/ video)

    Good luck!

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