If you have a BH76/77 with Thumb

[Monster5601]

Have you noticed any resistance when parking or deploying your thumb?

I have a reoccurring issue with the pivot pin that holds the thumb and bucket to the dipper stick. The first time the pin snapped in half near the center of the pin. This past weekend, I felt resistance when I parked the thumb. I pulled the pin out and noticed the pin is no longer straight. This has my dealer stumped and I am wondering if I am the only one seeing this issue or if others are also seeing it but do not realize what the problem is, or if there is a problem.

The first time this happen to me I throught the thumb resistance was due to dirt in the thumb arm until I noticed the pin sticking out on one side. That is when I discovered the pin had snapped in half destroying the dipper stick, thumb, and bucket. All were replaced under warranty but here I go again.

 

[hawkeye08]

I wonder if this guy has a thumb on his?? (just saw the website, I am not involved with it)

Kubota customer satisfaction information site

 

[jim_wilson]

Hmmm.. I have a BH77 on my B3200 and I haven't seen anything like that.

I haven't actually used the thumb all that much though. This weekend I swapped out the bucket for a ripper tooth from Michigan Iron - and I was able to knock the pin out relatively easily by using a wooden dowel and a mallet.

Sounds like you're going to have to some diagnosis/analysis on this to figure out what's buggering up that cross pin.

How often do you use the thumb? - and what do you use it for? Is the thumb bent and putting some weird forces into the pin?

 

[dfkrug]

I have a reoccurring issue with the pivot pin that holds the thumb and bucket
to the dipper stick.

So the thumb and bucket share the same pivot pin at the end of the dipper? The pin looks to be
a 25mm pin as used on other Kubota hoes of this size.

IMO, this is a bad design, esp for tractors that can put out 2500psi. The thumb pivots outside of
the bucket, which allows too much bending moment on the pin. For that design to work, the pin
should be at least 30mm and not have a grease groove.

This is also true for the shared dipper-cyl/boom-cyl pin on newer curvy-boom hoes. We are starting
to see some broken pins there, too.

 

[WaxMan]

I wonder if that is why there is a shortage of B77 hoes

 

[rScotty]

Have you noticed any resistance when parking or deploying your thumb?

I have a reoccurring issue with the pivot pin that holds the thumb and bucket to the dipper stick.
The first time this happen to me I thought the thumb resistance was due to dirt in the thumb arm until I noticed the pin sticking out on one side. That is when I discovered the pin had snapped in half destroying the dipper stick, thumb, and bucket. All were replaced under warranty but here I go again.

Twice is too often. That bend means that the pin is too small diameter for the stress and geometry. I assume it is a standard low carbon mild steel. What I would do is take the pin down to your local machine shop and explain the problem. The machinist will be able to roughly identify if yours is mild steel. If it is, ask him to make you a simple replacement pin of higher strength steel. There are much stronger steels and he probably has them right there on his material rack. It won't cost much, and will take twice the stress without bending.

At first I'd go with a standard solid pin without the grease slot and count on hand-greasing it periodically - at least until you see if you have a fix and monitor the wear. That should take care of the pin problem, but when something is under-designed it isn't unusual to have to replace several things in succession.

Still, this is an easy fix to that point. And it gives Kubota's tech dept. time to publish an upgrade.
rScotty

 

[jim_wilson]

Don't know if this means anything or not - but the BT820 hoe that is used on the B26 tractors - has a pin at the end of the dipperstick (pin that the bucket and the grapple both pivot on) - that is something 1.250" in diameter.

So obviously Kubota upgraded the BT820 for some reason with a bigger pin. Other than that - the two hoes are VERY similar dimension wise.

The old BT800 hoe that was on the B21 tractors - actually uses the same buckets at the BH77 - (so it has the same 1" or 25mm pin at the end of the dipperstick) - and I don't recall hearing anything about those hoes being a big problem. I would think on a contractor tractor like that if people were constantly breaking pins it would be something that would show up here on TBN with regularity.

 

[dfkrug]

The old BT800 hoe that was on the B21 tractors - actually uses the same buckets at the
BH77 - (so it has the same 1" or 25mm pin at the end of the dipperstick) - and I don't recall hearing anything about
those hoes being a big problem. I would think on a contractor tractor like that if people were constantly breaking pins
it would be something that would show up here on TBN with regularity.

Yeah, I had a B21 with the BT751 hoe that came with it. It did have 25mm pins, which were adequate for
the duty it served. BUT. There was no thumb option for the BT751, so none of the bending problems I
mentioned. Also, the B21 put out only about 2100psi. The pins did not have grease grooves as I recall.

Finally, Kubota uses hard steel pins, not mild ones. I have bought them new in the past from the dealer.
I prefer the mild steel ones myself. I can't say ALL Kubotas pins are hard/tough, so I can not say for
sure what's on the BH77.