Backhoe thumb retrofit

[bobsphotos]

Speaking to the idea that the pins are installed incorrectly, they are not. The pin for the hyd cylinder is installed exactly as the manual tube was installed. There are no extra holes. The unit is a weldment and given the fact that the hoe is still under warranty, i would not start changing things .I have included some pics to show the setup. I have also included a woods / Kubota 9' hoe setup with the hydraulic thumb.

 

[J_J]

I now see what you are talking about . You are right. That is an odd way to connect the rod end. As I said before, mine has three holes for mounting the cyl, and the closest one to the pivot point will generate the lesser force. It looks like you will have to install the relief valve, or bore some new holes for the thumb. Another option is to change out the cyl for one that is not as strong.

 

[bobsphotos]

Thanks to all. The relief valve has been ordered and I will update the post after I get it istalled.
Bob

 

[CurlyDave]

It is not entirely obvious to me that you want to make this change.

There has been many a time when I wanted to change the angle of the thumb while holding up a rock and just being able to push the bucket back by activating the thumb would have been very helpful in that situation.

The problem with moving the bucket away from the thumb while moving the thumb toward the retreating bucket is that is easy to drop the rock if you get the least little bit out of sync.

Of course the cat's meow would be to have the thumb overcome the bucket while the thumb is moving forward and the bucket overcome the thumb while the bucket is moving forward.

If anyone comes up with how to do that I am all ears.

 

[bobsphotos]

Hi Dave,
My concern is more that I am damaging something by driving the bucket cylinder backwards. Since you cannot compress fluid, it has to be going somewhere and I don't know enough about hydraulics to understand what is happening and where the fluid is going. I think it is also an issue that the movement is creating cavitation in the opposite circuit.

 

[J_J]

My thoughts on this, is that if the valve and cyl are good, and the linkage is tight, and since hyd fluid does not compress easily, in order to cause the cyl rod to compress or retract in the cyl, the fluid and piston is trying to compress air in the cylinder. That to me is the only logical answer I can think of..

When a valve closes off the cyl ports, the cyl should remain stationary, so,

If you are pushing the cyl back, and it returns after you release the thumb, what force would cause the rod to push back with no fluid power, except air. I believe the other side of the cyl has an air bubble, because the valve has shut off all fluid transfer to the bucket. No fluid in or out.

If the linkage is tight, it will by itself not cause the rod to retract. Mechanical linkage can cause damage as I believe Carl in the Power-Trac forum just bent his cyl rod on his Power-Trac., because of a mechanical advantage. Applied more back force than the cyl could take.

 

[bobsphotos]

JJ,
If I bring the thumb against the bucket and then move it another inch or so and then release it, the bucket snaps back as if it had compressed some air. But, if I bring the thumb against the bucket and move it another 5 inches, and then release the thumb, the bucket stays. Mystery to me........My feeling is that it has to be dumping fluid somewhere.

 

[J_J]

Does your valve have work port relief? If so, that would explain where the fluid went, because the thumb cyl pushing on the bucket, cause the BH cyl to generate enough force to push fluid past the relief. If no relief valve, then the fluid is being pushed past the spools. If you were to put a hyd gage on the bucket cyl, you would see what is happening,

That inch or two, is that at the tip of the bucket? I believe that would be normal. But not 5 in.

 

[kennyd]

JJ,
If I bring the thumb against the bucket and then move it another inch or so and then release it, the bucket snaps back as if it had compressed some air. But, if I bring the thumb against the bucket and move it another 5 inches, and then release the thumb, the bucket stays. Mystery to me........My feeling is that it has to be dumping fluid somewhere.

It could also be that the lines are expanding ever so slightly to take up the pressure rather than air.

 

[AKKAMAAN]

Here is a pdf link to download the woods BH80x backhoe manual......your problem is to be tracked in the original control valve, which is loaded with port relief valves according to this manual.....see page 23-27...

You are saying the bucket returns after being pushed one inch.......I am sure that is a play in the linkage....