Hydraulics Grey Beard needed; help with a backhoe control valve alternative

[ChilemanX4]

I have an old B20 with a BT750AR backhoe (http://www.tractordata.com/backhoe-loader/000/1/3/130-kubota-b20.html). The backhoe has a auto return feature which is electronical controlled. One of the electrical solenoids (yellow) came apart. I am not sure if the solenoid is the failure point or a symptom of another failure. The original control valve part number is 78621-63010. Due to the inoperable auto return function and age/wear, I would like to find a non-electric alternative. Any advice on where to start?

 

[GreensvilleJay]

trying to help....
will the BH still function with the manual levers fine ?
As in you do NOT HAVE to have the 'auto return' feature ?
are both solenoids the same part ? looks like number 460 ? in the fuzzy picture.
can you take/show picture of the broken solenoid ?
Is there a part number for the solenoid ONLY ($460 ?) ?

 

[kubotafreak]

trying to help....
will the BH still function with the manual levers fine ?
As in you do NOT HAVE to have the 'auto return' feature ?
are both solenoids the same part ? looks like number 460 ? in the fuzzy picture.
can you take/show picture of the broken solenoid ?
Is there a part number for the solenoid ONLY ($460 ?) ?

Probably do when the solenoid is in place properly. If it came apart, your out of luck because they are opposing forces. This solenoid takes the place of the standard spring center cap.


OP,
If you check the parts diagrams, there should be a non solenoid version. The lever pivot should be available to eliminate the solenoid to grab the spool. You will also need the spring center bottom assembly, and top seal holder as well. Wont be cheap, valve components are pricy. Other alternative is to see if you can source the spec numbers off that solenoid. Kubota more than likely didn't one off that part, being it is so old.
Or the easy way, just pay the high price Kubota wants and be done with it.

 

[TheOldHokie]

I have an old B20 with a BT750AR backhoe (http://www.tractordata.com/backhoe-loader/000/1/3/130-kubota-b20.html). The backhoe has a auto return feature which is electronical controlled. One of the electrical solenoids (yellow) came apart. I am not sure if the solenoid is the failure point or a symptom of another failure. The original control valve part number is 78621-63010. Due to the inoperable auto return function and age/wear, I would like to find a non-electric alternative. Any advice on where to start?

View attachment 74549 View attachment 74550 View attachment 74551

Off the top of my head:

That is just one valve in the stack. Assuming it is not leaking purchase a new valve of your choosing - I would go with a solenoid actuated type,. Mount it in the general vicinity of the backhoe stack, and plumb it into the outlet line from the backhoe valve. Then move the work ports and electrical connections on the FUBARed auto return section in the backhoe valve to the replacement and plug the work ports on the FUBARed section. . Done.

Ooops - I think I may have misunderstood what teh solenoid does....... Perhaps you could educate me on how that function works.

Dan

 

[kubotafreak]

Off the top of my head:

That is just one valve in the stack. Assuming it is not leaking purchase a new valve of your choosing - I would go with a solenoid actuated type,. Mount it in the general vicinity of the backhoe stack, and plumb it into the outlet line from the backhoe valve. Then move the work ports and electrical connections on the FUBARed auto return section in the backhoe valve to the replacement and plug the work ports on the FUBARed section. . Done.

Ooops - I think I may have misunderstood what teh solenoid does....... Perhaps you could educate me on how that function works.

Dan

If the solenoids are in place the lever works manual. The solenoids on both ends use opposing force to move the spool. Issue I assume he is having is the lower one decided to grenade. Without good solenoids or spring pack, the spool wont center correctly.

Ive found the parts you need, you will be in much more $ to convert to manual than fix what you got. Look up BT750C. It is the manual equivalent. You would need spring cap 75540-61470 and left linkage 75592-71140 with small parts. Also you might run into issue with the valve spacer needing to be removed. That would require the left mount holes to be made larger.

 

[TheOldHokie]

If the solenoids are in place the lever works manual. The solenoids on both ends use opposing force to move the spool. Issue I assume he is having is the lower one decided to grenade. Without good solenoids or spring pack, the spool wont center correctly.

I understand how a solenoid valve works. I dont understand what it does in this application. If it is just an independent DA valve in the stack then my initial idea should work.

Dan

 

[kubotafreak]

I understand how a solenoid valve works. I dont understand what it does in this application. If it is just an independent DA valve in the stack then my initial idea should work.

Dan

If you don't go with factory, the aftermarket wont fit in the stack. It is my understanding he wants to get away from the brain box/solenoid input. The thing works like a normal one, with mechanical pass through the top solenoid. The brain box then calculates a timed event to bring the backhoe back to home.

 

[TheOldHokie]

If you don't go with factory, the aftermarket wont fit in the stack. It is my understanding he wants to get away from the brain box/solenoid input. The thing works like a normal one, with mechanical pass through the top solenoid. The brain box then calculates a timed event to bring the backhoe back to home.

I am not trying to fit anything into the stack and I still dont understand the function. The top solenoid appears to have some sort of mechanical linkage connecting it to the joystick. What does that do?

If all he wants to do is disable the function just remove the solenoid section from the stack.

Dan

 

[TheOldHokie]

I am not trying to fit anything into the stack and I still dont understand the function. The top solenoid appears to have some sort of mechanical linkage connecting it to the joystick. What does that do?

If all he wants to do is disable the function just remove the solenoid section from the stack.

Dan

So I took a look at the parts diagrams - not a lot of help with the plumbing but it seems there is a swing position sensor mounted on the boom that presumably provides the input signal for the electronic controller. I could find nothing related to the solenoid valves hydraulic connections. I assume that valve is simply plumbed in parallel with the manual valve and either one of them can actuate the swing cylinders???

So a AR delete would simply require the removal or disabling of the solenoid valve. The backhoe valve is a stack valve and the solenoid section is the last one in the stack. Can you not simply remove it and run fully manual? If can't be removed I would think one could find a way to lock that spool in the neutral position - maybe a couple shaft collars?

If you wanted to retain the AR function what is wrong with my original suggestion of mounting a vanilla solenoid valve on the bulkhead and plumbing it in as a "5th function" supplied by the output section on the OEM valve.? You would still have to remove or disable the OEM solenoid section as in a delete.

Dan

 

[ChilemanX4]

trying to help....
will the BH still function with the manual levers fine ? No it swings to one side
As in you do NOT HAVE to have the 'auto return' feature ? The "auto return has not worked since I have had it. The BH functioned fine until the top of the solenoid came off, and oil start spilling out. The oil wasn't coming out under high pressure, but there was a lot so I assume large hole.
are both solenoids the same part ? No, they have different part numbers.

looks like number 460 ? in the fuzzy picture. 440 & 460 called yellow and green solenoid
can you take/show picture of the broken solenoid ? Attached, It appears to be just a press fit. There is nothing holding the solenoid together.
Is there a part number for the solenoid ONLY ($460 ?) ? The part is no longer available

 

[ChilemanX4]

Off the top of my head:

That is just one valve in the stack. Assuming it is not leaking purchase a new valve of your choosing - I would go with a solenoid actuated type,. Mount it in the general vicinity of the backhoe stack, and plumb it into the outlet line from the backhoe valve. Then move the work ports and electrical connections on the FUBARed auto return section in the backhoe valve to the replacement and plug the work ports on the FUBARed section. . Done.

Ooops - I think I may have misunderstood what teh solenoid does....... Perhaps you could educate me on how that function works.

Dan

There is a sensor on the swing arm. Based on where you set home the controller will auto swing the bucket back to home position. It uses the solenoids to activate the valve, I wouldn't trust hooking up a different valve in the current controller to operate as expected.

 

[ChilemanX4]

If the solenoids are in place the lever works manual. The solenoids on both ends use opposing force to move the spool. Issue I assume he is having is the lower one decided to grenade. Without good solenoids or spring pack, the spool wont center correctly. That is correct.

Ive found the parts you need, you will be in much more $ to convert to manual than fix what you got. Look up BT750C. It is the manual equivalent. You would need spring cap 75540-61470 and left linkage 75592-71140 with small parts. Also you might run into issue with the valve spacer needing to be removed. That would require the left mount holes to be made larger.

I will have to see if these parts are still available. I would also consider a after market assemble.

 

[ChilemanX4]

I am not trying to fit anything into the stack and I still dont understand the function. The top solenoid appears to have some sort of mechanical linkage connecting it to the joystick. What does that do?

If all he wants to do is disable the function just remove the solenoid section from the stack.

Dan

I assume the linkage is attached to some kind of potentiometer to send signal to solenoid based on lever movement. ( I could be misunderstanding the circuit as well).

 

[ChilemanX4]

So I took a look at the parts diagrams - not a lot of help with the plumbing but it seems there is a swing position sensor mounted on the boom that presumably provides the input signal for the electronic controller. I could find nothing related to the solenoid valves hydraulic connections. I assume that valve is simply plumbed in parallel with the manual valve and either one of them can actuate the swing cylinders??? That is the way I understand it.

So a AR delete would simply require the removal or disabling of the solenoid valve. The backhoe valve is a stack valve and the solenoid section is the last one in the stack. Can you not simply remove it and run fully manual? That is what I would like to do, but I need the linkage and not sure what would replace the solenoids. If can't be removed I would think one could find a way to lock that spool in the neutral position - maybe a couple shaft collars?

If you wanted to retain the AR function what is wrong with my original suggestion of mounting a vanilla solenoid valve on the bulkhead and plumbing it in as a "5th function" supplied by the output section on the OEM valve.? You would still have to remove or disable the OEM solenoid section as in a delete. I am not interested in maintaining the AR function

Dan

 

[GreensvilleJay]

hmm.. sound like when the solenoid broke, the 'core', the sliding steel piece that the 'coil' moves when power is applied, came OUT of the actual 'control valve' body. If so, 'silly' design. No oil should come out as the 'inner' pieces shouldn't be able to come out.
hard to explain but I was thinking the solenoid core was attached like a control lever was.
I'd need much better drawing to se WHY oil came out and a possible fix.
Not to sure WHY you 'need' a computer to run the BH...sounds like a $$$, nasty way to run it.

 

[TheOldHokie]

It looks to me like you can just take the entire solenoid section out of the stack and run the valve as is. What linkages need to be changed?

Dan

 

[ChilemanX4]

It looks to me like you can just take the entire solenoid section out of the stack and run the valve as is. What linkages need to be changed?

Dan

Replace the electrically controlled swing section with a manual control and linkage.

 

[ChilemanX4]

hmm.. sound like when the solenoid broke, the 'core', the sliding steel piece that the 'coil' moves when power is applied, came OUT of the actual 'control valve' body. If so, 'silly' design. No oil should come out as the 'inner' pieces shouldn't be able to come out.
hard to explain but I was thinking the solenoid core was attached like a control lever was.
I'd need much better drawing to se WHY oil came out and a possible fix.
Not to sure WHY you 'need' a computer to run the BH...sounds like a $$$, nasty way to run it.

 

[TheOldHokie]

Replace the electrically controlled swing section with a manual control and linkage.

I thought you simply wanted AR deleted.

Dan

 

[ChilemanX4]

I thought you simply wanted AR deleted.

Dan

Sorry I should of said. replace the electronic control.