Kubota BH92 Weak Boom Hydraulics

[OttoOrange]

I have a L3560 HST Cab with LA805 loader and BH92 Backhoe. FEL works fine. The boom on the backhoe is very reluctant to retract when fully extended with dipperstick also at full reach, without a load in the bucket. When partially loaded, the only way the boom will lift seems to be if I curl the bucket and retract/drag the dipperstick back closer to the machine. Dipperstick and bucket seem to be working fine. Swing is also okay. Stabilizers are good although seem a little less able to lift the back of the machine than they initially could.

The backhoe was "used", sat in the dealer's lot for ??? (maybe a year or so. Original owner traded it in on a snowblower, had purchased the BH in 2015). The dealer installed a hydraulic thumb which seems to work fine, although with the weak boom it hasn't had much of a workout. When operating the bucket and dipperstick at the same time, they both move at the same time. Anytime the boom function is engaged with any other function like swing or dipperstick, the boom just stops responding. Needless to say flat, level trench bottoms are a real challenge. HST fluid is in the dipstick range and machine has just over 20 hours. All grease fittings have been greased twice. I changed the bucket from a 16" digger to a 24" ditching (no teeth) bucket and the extra weight of the bigger bucket is noticeable on the boom function. All functions seem to work at initial machine startup but as it warms up, the boom malfunctioning is more evident. The cylinders seem to get warm but not really hot.

With the tractor off and the bucket, dipperstick and boom all curled in tight, the bucket hits the ground in about 6 hours. With the boom and dipperstick fully extended and bucket half curled, the bucket falls 30" in about 2.5 hours. Stabilizers only drop about 1" overnight.

Any suggestions and insights are greatly appreciated. Thanks.

 

[art]

I would talk with the dealer that you bought it from to get the valve body fixed.

 

[4570Man]

My BH90 did the same thing. It’s got a spring on the bottom of the valve and a cup around the spring and plunger. There’s an oring on the valve plunge. When the o ring leaks it fills up the cup with fluid and prevents the valve plunger from moving. The bandaid fix is to drill a hole in the cup so the fluid drains. The proper fix is tear the whole thing apart and put new o rings in it.

 

[OttoOrange]

I would talk with the dealer that you bought it from to get the valve body fixed.

Yeah thanks. I have a call into the Service Dept of the dealer, waiting to set something up. Is the valve body you refer to on the boom cylinder or the control stick. Sorry, my first tractor and not very savvy about hydraulics.

 

[4570Man]

Yeah thanks. I have a call into the Service Dept of the dealer, waiting to set something up. Is the valve body you refer to on the boom cylinder or the control stick. Sorry, my first tractor and not very savvy about hydraulics.

The backhoe will have the whole thing bolted together on one stack.

 

[ericm979]

The control joysticks and levers operate valves which direct the flow of oil to the cylinders.

 

[rScotty]

Is the valve body you refer to on the boom cylinder or the control stick. Sorry, my first tractor and not very savvy about hydraulics.

The backhoe will have the whole thing bolted together on one stack.

I believe the valve body he is referring to would be one of the valves within the stack of control valves that are worked by the control stick(s). The valves for a backhoe are often held together as a a group stacked together horizontally and made into a single stack of valves stack through bolts. This stacked valve body would be close to your knees rather than out on the boom.
rScotty

 

[OttoOrange]

Service tech came yesterday. Did 3 hydraulic pressure checks at different points and got the same reading, about 1600 psi I think. Then reconfigured the joystick controls to "Excavator " and got the same boom problem on a different control stick. Removed the boom cylinder to take to the shop for further investigation.

So I guess that is progress. Now waiting again with the tractor out of commission. Didn't remove the backhoe as I don't have much to do with just the front end loader anyway.

 

[OttoOrange]

A week after the service guy took the boom cylinder to the Shop, I finally phoned to check on its status. The Service Manager (I assume) said the following:

Apparently the cylinder is fine and really didn't have to be removed from the machine. The backhoe is supposed to operate like that. The BH77 in the Yard does the same thing ... you need to feather the controls so that one control doesn't "get" all the power. If I am around tomorrow he and the salesman will bring out the cylinder and re-install it, but will call first before they come.

That was 2 days ago. Yesterday, no phonecalls and no show. Today the same thing. I have read in other threads how much trouble some owners have had getting any satisfaction from their Kubota Dealer, and now it's happening to me. Do I really need to be the "squeaky wheel", always phoning and complaining? I guess so. It's been 21 days since I first phoned "service" and explained my problem. He was going to call me back. Never happened.

Is the BH92 backhoe really supposed to only operate one control at a time? That sure isn't what the Manual says: "With experience, the combination of both "joystick" levers will allow lift, swing, crowd out and spoil dumping, all in one smooth movement, or lowering, swing, crowd in and bucket filling with reverse movement."

I know this isn't a $300,00 HyHoe, but geez louise when the boom control by itself won't even pick up the fully extended, empty bucket and arm something must be wrong.

I guess I need a crash course in Tractor Hydraulics. I'm sure there is some good info on TBN. Any ideas or suggestions on how to proceed would certainly be appreciated.

Thanks.

 

[ericm979]

Your first post described something different from operating two controls at once- it sounded like the boom was weak when operated by itself. Sorry your dealer's not on the ball. You'll just have to call and remind them. It's unfortunate but a lot of people operate like that.

I only have a few hours on it but my Branson backhoe is pretty difficult for me to operate two cylinders at once and do it smoothly. Regular tractor backhoe hydraulics are not that sophisticated. I got a chance to run a mid size Kubota excavator for a short time not long ago and it was amazing how much better the controls are. But they're expensive proportional electric over hydraulic controls, not relatively simple manual valves like tractor backhoes have.

I'm sure practice will improve my abilities on the Branson backhoe. One thing that will help with moving two cylinders at once is running the tractor at a high enough RPM. Some people recommend new operators use a low rpm to slow the reactions but that also means lower hydraulic flow, which might not be enough for multiple cylinders.

In basic hydraulic systems when you operate two cylinders at once, the one that has the least restriction on it will move first. I can see that with my BH when I try to curl and move the boom in. Depending on where the bucket and dirt is, one or the other function will move.

My BH's boom was moving too fast and the valve was not easy to feather, so I put adjustable restrictors on it to slow down the maximum speed.