Thumb Ideal Thumb size

[Chilliwack Murray]

I’m going to put a weld on mechanical thumb on my Kubota 4672 backhoe - probably a Titan and there are a few guides that show measuring the bucket length from pin to tip of the teeth and selecting that thumb. These same instructions also state the importance of exactly the right length thumb but don’t give any other guidance.

With my bucket at 90 degrees, the required thumb would be about 26”. There are 24 and 32” thumbs available but I’m looking for some advice from those who use them on the ideal size.

Is a 24” that would reach the end of the bucket, not the teeth correct or is a 32” that would extend 6” beyond a better choice? There is a it of a weight penalty for the 32”
and the 4672 is a pretty small operation already which is why I’m looking at weld on vs a clamp on.

Thanks in advance for any input.

 

[nyone]

Get the 24. Your trying to hold things in the bucket not in the thumb.

 

[Sysop]

I recently went through the same thing. In my research, I found some instances of "universal thumbs" causing the destruction of some small tractor hoes. In particular, the ones that attach midway up the arm of the tractor. What happens is, the steel of the arm isn't intended to have a pressure point added mid-way and when the bucket closes against the thumb, it puts a slight buckle in the steel.

https://www.tractorbynet.com/forums/attachments/128216-kubota-bh75-damaged-bolt-thumb.html

If your BH does have a thumb option available, I advise going that route. I had to spend twice as much on one as one of the universal ones, but it fits my BH as the engineers intended.

 

[Chilliwack Murray]

Thanks, that’s the kind of info I was looking for but just couldn’t find.

Unfortunately most of the photos are gone but at least it described the issue well and makes perfect sense when you think about it. I may still use the Titan thumb but fab a brace bracket as high up the stick as possible.

 

[Chilliwack Murray]

So I did order the 24" Titan thumb and as it turns out, the mounting plate pretty much spans the length of the dipper stick so there is no real concern of bending.

I did find that the original pin locations didn't appear to allow the thumb to extend far enough in my opinion so I added another set on the brace mounting and the thumb pivot point. Installed it yesterday and quite happy with the results, and surprised how much it can lift.... If the bucket and thumb can get around it, it will hold and lift it without an issue. I can see that it would be easy to tip the tractor if you made sudden movements holding a large rock, with the boom at maximum swing but there are lots of ways to tip a tractor.

Pretty happy over all, I may notch the bottom of the thumb for the centre tooth at some point so it will close against the shell of the bucket but so far it seems to do quite well. I may try making one for the JD400, it would be nice to be able to lift 1000lb rocks and have more reach but for $150 I am very happy with this.

 

[Gary Fowler]

Your thumb should close against the teeth of your bucket. Yours looks to be a little short to do that, likely you need to move the mounting closer to the pivot point of your bucket for that to happen.
Also, when it is retracted, it should come back far enough so that it wont interfere with using the bucket to dig. This would mean it should lay practically flat against the dipper stick.

 

[Chilliwack Murray]

The thumb actually extends beyond the teeth using the original mount holes depending on the angle it is set at which was why I cut the second set. It’s more obvious in this photo :



I think it’ll be more versatile if I notch it to close into the tooth but I’ll use it a little more before I make any more changed.

I can move it to the original mounting holes at the end of the bracket and it would fold flat but I really don’t intend to leave it in place when I’m not using it. Two pins and it’s gone:



It’s unfortunate that none of the people who sell thumbs give much info on sizing or even locating them correctly. That was the reason I started this thread and even at that, only got one reply... until after it was mounted of course.

It seems to me the brace could be a few inches longer so the thumb would point straight down without adding the last set of holes. I’ll probably make a longer brace at some point.

 

[CADplans]

Every answer, and a demo of that answer is in this video,,,

You will see why getting the right length is critical,,,

 

[mpsmith60]

I just recently bought the BXpanded Barracuda Factory Fit Thumb for my BH77 backhoe. It is specifically designed for my backhoe. I chose it over a Kubota OEM thumb for three reasons:

1. The BXpanded thumb costs less.
2. I felt the BXpanded design with the curved jaw was better.
3. This one is the "long jaw" version which was specifically designed to work properly with my BXpanded quick-on bucket connect so that the thumb meshes properly with the bucket edge and teeth. There is a shorter version for folks without the quick-on bucket connect.

Attached is a picture of the thumb and how it meshes with my 16" bucket and BXpanded Quick-on Bucket Connect, which makes switching to my trencher bucket or ripper tooth really quick and easy.

Here is a video of me installing, and testing the thumb for anyone interested:
BXpanded Backhoe Thumb for My Kubota - YouTube

This thumb fits the BH65, BH70, BH76, and BH77 Kubota backhoes. You'll see in the video why I highly recommend it.

 

[MikeInEburg]

I just ordered the BXPanded thumb, and am anxiously waiting for it to join the other BXProducts that I already own.