Backhoe Kubota 4560 backhoe boom will not rise

[Airdriver]

This 4560 3 pt backhoe, with its own hyd pump on the pto, is on a L3560, all built in the early 90's.

Had to remove and repair the pump this summer as the connector to the 3 pth was worn and pump wobbled significantly on it. So the backhoe has not been powered for about 5 months.

Finally got the 3 ph connection fixed, changed the filter, primed hyd pump, filled the hyd resevoir with (about 5 gal) fluid, started the tractor and engaged the pto. Everthing works but the lift for the main boom. The control handle for the boom seemed to stick when I first moved it to lift the boom, but moved freely once activated. Handle works to lower the boom. The hyd pump labors when lift handle is pulled back. Sometimes it lifts the boom a fraction of an inch, where it stays. Used other tractor to lift the boom so I could reinstall the keeper pin.

There are no quick disconnects and no obvious leaks or faulty hoses.

The four operating handles (two for boom & bucket, two for stabilizers) are connected to a single manifold.

The hyd cylinder and hoses to lift the boom are inside the boom body.

Any suggestions as to where to turn?

Many thanks, Airdriver

 

[art]

Sounds like you need to pull the valve apart!

 

[Grandad4]

I have the same 4560 hoe, Airdriver. Wish I could give you more specific advice, but the best I can offer is to support what Art says: it's probably in the valve block, either debris obstructing that circuit or the valve itself is on the fritz. Probably not in the lines because the boom does move in the other direction. The fact the control seemed stuck when you first tried to move it would suggest it's the valve also. Has it been exposed to the elements over the summer? If so, there's a possibility that moisture got into the valve block and caused rust issues; otherwise it might just be from 20+ years of wear.

That's a good old, heavy-duty backhoe. Hope you can get it back in working order without breaking the bank.

 

[bumperm]

What those guys said.

Also check the joystick control linkages for looseness and wear. Enough wear, or a loose ball end nut, can cause enough slack that the valve spindle does not move enough to open the port. You'll be taking the coves off to check the spool valves anyway, so this is easy enough to eliminate at the same time. If all the other cylinders operate, and with *force* (i.e. you can lift the hoe with the stabilizers, not just have them move both ways, then that eliminates the pump itself at the cause. I say this as the boom cylinder has probably the most weight to move just lifting it, so a very week internally bypassing pump that results in low pressure could conceivably cause just the boom not to lift (but then the stabilizers wouldn't lift the hoe either).

 

[Airdriver]

I have the same 4560 hoe, Airdriver. Wish I could give you more specific advice, but the best I can offer is to support what Art says: it's probably in the valve block, either debris obstructing that circuit or the valve itself is on the fritz. Probably not in the lines because the boom does move in the other direction. The fact the control seemed stuck when you first tried to move it would suggest it's the valve also. Has it been exposed to the elements over the summer? If so, there's a possibility that moisture got into the valve block and caused rust issues; otherwise it might just be from 20+ years of wear.

That's a good old, heavy-duty backhoe. Hope you can get it back in working order without breaking the bank.

Thank you all for the suggestions.

I cringed at the valve block. It looks like there is a lot going on in there. Not pretty, but it does an awful lot around here that would be very difficult otherwise. When I get the time, I will pull it apart.

If anyone has done this before, is there anything I should know about before I start?

Again, many thanks.

 

[Airdriver]

Running the tractor at max rpm, I got the boom to rise, 2" at a time. Thinking Pump must be worn out as everything moves slowly, way more slowly than before.

But what is the psi and gpm of that pump? Mine is missing the info.

Many thanks

 

[Grandad4]

Running the tractor at max rpm, I got the boom to rise, 2" at a time. Thinking Pump must be worn out as everything moves slowly, way more slowly than before.

But what is the psi and gpm of that pump? Mine is missing the info.

Many thanks

I'll see if I have any info at the shop in the morning and reply.

 

[bumperm]

Running the tractor at max rpm, I got the boom to rise, 2" at a time. Thinking Pump must be worn out as everything moves slowly, way more slowly than before.

But what is the psi and gpm of that pump? Mine is missing the info.

Many thanks

Hmmm, I'm pushin' 71 and move a little slow when I start out too. Can tractors suffer a "pump attack"? My pressure is good 110 / 60 or so, so I'm not looking for a pump attack any time soon - I hope.

A pressure gauge and fittings to attach isn't very expensive. Typical tractor hydraulic pressure runs from about 2000 psi on the really small ones, to over 3000 on the big ones. My B series Kubota specs at 2450 psi.

 

[Grandad4]

I'll see if I have any info at the shop in the morning and reply.

Sorry to say that neither the owners manual nor the bh/pto pump units show any information. Can only suggest someone in the service dept at a Kubota dealer should have or could get that information.
Is reservoir full? Filter not clogged? Have you tested the pressure?

 

[dfkrug]

Running the tractor at max rpm, I got the boom to rise, 2" at a time.
Thinking Pump must be worn out as everything moves slowly, way more slowly than before.

First get the pressure gauge and see what is happening. Your pump may be delivering
full pressure, but all the oil is going thru the relief valve.

If you have the valve stack exposed, you can tell if the RV is activated if you put
your finger on it when you pull one of the levers.

Anyway, these self-contained systems that are stored outside often suffer from
hydraulics problems as they are not sealed from the environment. Contamination/
condensation gets into the oil reservoir.

If you do have to take the valve apart, the biggest job will be taking off all the
hoses and keeping track of where they connect. Your valve is probably a
"stack valve" and it is held together by 4 threaded rods.