JD 448 backhoe - anyone add a thumb?

   / JD 448 backhoe - anyone add a thumb? #11  
Here are a few pics showing the thumb on my 48 backhoe. It has performed flawlessly for several years and is a critical feature on this machine whenever I use it. There are rocks everywhere here, so every time I have to do any digging, it’s super handy to be able to pick them up, versus wrangling to get them balanced in the bucket alone. And being able to handle small to medium sized logs is also a benefit. If I had to do it again, I would do exactly the same thing.
 

Attachments

  • 85F964F4-4B0C-422F-B062-2BCDF39B93F5.jpeg
    85F964F4-4B0C-422F-B062-2BCDF39B93F5.jpeg
    5.4 MB · Views: 130
  • B8AFDF9F-A0E6-4258-AC1C-E41962388D7F.jpeg
    B8AFDF9F-A0E6-4258-AC1C-E41962388D7F.jpeg
    4.2 MB · Views: 139
  • FE9AC584-CF61-4A36-967F-EDED6C22811E.jpeg
    FE9AC584-CF61-4A36-967F-EDED6C22811E.jpeg
    4.3 MB · Views: 144
   / JD 448 backhoe - anyone add a thumb? #12  
Thank you for your reply. So I went on line and I found a single pole control valve. It is very much like my double pole control vale that I have from my old plow setup but I ordered the new one. Where did you get the fluid from to run the system? I thought that I could pick up the supply and return lines by placing tee's where the Poser Beyond supply and return lines go into and out of the JD control lines come out of the control valve setup underneath the the control valves on the tractor. What I would like to do is have a foot activation for the Frod. Thank you again
 
   / JD 448 backhoe - anyone add a thumb? #13  
Hidden: I think I used a Prince valve, which was around $150. I selected this one because it has a work port relief and also a power beyond port. Both of those are very important. I also selected it because it's a segmented valve and gives me the opportunity to add a second spool sometime in the future for something else. It's all detailed in the thread I referenced. Please read that since it has a tremendous amount of info about the design. I had to learn a great deal while doing this and all that is covered there.

The valve is inserted into the tractor power beyond line that runs the backhoe. So the tractor feeds the new valve, and the power beyond port in the new valve feeds the backhoe. So when you are running the thumb, it will interrupt the operation of the backhoe. I have found that when I'm lowering the boom, that this is a good time to extend the thumb if needed. I think the pressure created by the weight of the boom make it possible to make both motions at the same time. The work port relief is important because it creates a relief point for when the bucket pushes against the thumb. I was particularly concerned that when the thumb and bucket push against each other, that in some positions there could be mechanical advantage that could lead to excessive hydraulic pressure, and something could blow.

In my thread, you'll see the details of how the spool valve is mounted and how it's foot operated. I was going to add some kind of pedal, but the way it's set up now works perfectly and doesn't need anything more. I can lift to retract, and push to extend, which is quite intuitive.
 
   / JD 448 backhoe - anyone add a thumb? #14  
   / JD 448 backhoe - anyone add a thumb? #15  
Yes. You need to insert the new thumb valve into the tractor’s power beyond line that now feeds the backhoe. The backhoe is then fed by the power beyond port in the new valve. This will give the thumb priority over the backhoe and interrupt the operation of the backhoe any time you are moving the thumb. However, I have found that I can time my thumb movements any time I am lowering the boom. This way the boom can be moving down, driven by its own weight while the thumb is extending out, driven by valve pressure in preparation to pick up a rock or something.
 

Tractor & Equipment Auctions

2015 FORD F750 26FT BOX TRUCK (A51219)
2015 FORD F750...
2014 MACK GU813 GRANITE ROLL OFF TRUCK (A50854)
2014 MACK GU813...
2012 CATERPILLAR 259B3 SKID STEER (A51242)
2012 CATERPILLAR...
2006 CHEVROLET SILVERADO 4X4 PICKUP TRUCK (A51222)
2006 CHEVROLET...
2024 MERCEDES-BENZ SPRINTER 3500XD BOX TRUCK (A51222)
2024 MERCEDES-BENZ...
2020 KUBOTA RTV X1100C UTV (A51406)
2020 KUBOTA RTV...
 
Top