BH75 Follow with pics

[grizzjeeper]

Last week I posted about the dipperstick arm twisting on my BH75 backhoe with less than 10 hours on it. The second failure in a year. The more I think about how this couls have happened under its own power, how fragile this must be and reading comments from others with thousands of hours with 0 breaks, I have determined there must be an issue with MY hoe. I mean I have barely used it...

The only conclusion that I can even come close to understanding the amount of damage done to the backhoe would be the amount of play in the dipper stick pin. I realize the ends of the pin are snug but the center section is not, possibly the hole is/was machines incorrectly? The key here is the amount of play that was there couldn’t possibly be from wear as the amount of hours does not depict that so I have to lean on the idea that something wasn’t right from the beginning. The more I think about this the more I feel this may be the cause. If there is lateral movement in the dipper stick arm then the geometry has changed, and I do not know how much the geometry can change before the design is overcome by the unexpected angle of pressure put forth. I feel that if the arm can twist to the left from a sloppy middle connect and you apply pressure the propensity for the arm to continue in that direction is greatly increased.



Now this leads to my next theory, is it possible that same sloppiness is what caused the other cylinder to break? I mean it’s the same idea just on the other end. That cylinder is pushing on an arm that has lateral movement and I know that the rod cannot have much movement before it breaks. I know there was an issue with those cylinders breaking but I now wonder if say there was a batch or arms that came out with pin hole’s inside diameter out of spec, subsequently creating a separate problem? Any thoughts on this?

 

[wushaw]

That is the same cylinder that I bent but not sideways...I don't see how that happened. Is there a broken pin for the bucket or is the bucket holes too big for the pins.
You must have some serious slop in there somewhere.

 

[dfkrug]

Now this leads to my next theory, is it possible that same sloppiness is what caused the other cylinder to break? I mean it’s the same idea just on the other end. That cylinder is pushing on an arm that has lateral movement and I know that the rod cannot have much movement before it breaks. I know there was an issue with those cylinders breaking but I now wonder if say there was a batch or arms that came out with pin hole’s inside diameter out of spec, subsequently creating a separate problem? Any thoughts on this?

Yes, GRIZZ, I think you are on the right track. If your pivot hole is too
large and not UNIFORMLY too large, extending the cylinder will put
lateral bending force on the cyl and rod. Pop goes the rod, when you
entend it. Pull out the pin and look the hole. Take some ID measurements.
Thx for posting the pix.

 

[MessickFarmEqu]

Did you ever mention what you where doing when this happened?

 

[Bob53]

Thanks for the pictures. Not sure where you are saying the sloppyness is but i see the size of you're bucket. my therory on this hoe or any hoe for that matter is the tougher the digging or using a bigger bucket like you'res the more important technique is to protect the hoe. this hoe's protection is only so good. My opion the BH75 protection although might be OK for most, its not as well protected as some others so you need to watch what you're doing. With the wider bucket seems like you would stress a little more if digging with the outside tooth on a wide bucket rather than a narrower bucket. futher away the stress is from corner to mid point more stress on the hoe. And if you're pin hole is a little sloppy too, just another stress on the hoe. They all add up to these failures.
i hope you're dealer takes care of you, good luck with you;re fix.

 

[grizzjeeper]

The bucket is what comes on all the bh75's

You can get an optional larger or smaller size.

I was digging up a 15 year old stump, not sure when it happened, I didnt notice it until I was done.

The Slop is where the dipperstick arm connects to the boom arm. The pin looks like the right size, bacause it is snug in the boom. Looks like the dipperstick arm has a larger ID than it should have, or there was not enouch shim? I notice a shim on each side...

 

[teachdocs]

Mr. Pit Bull seated in the background of pic 3 looks mighty suspicious.
Does he know how the BH got bent?
Maybe digging for a big dinosaur bone?
Hee Hee

 

[Jdengr]

That appears to be the same bucket (16") that I have on my BH75. I don't think there should be any noticable slop between the dipperstick and boom. Either lateral or on the pivot pin. There is none detectable on mine. I don't have a parts manual, but it is possible that the dipperstick would have a replaceable sleeve in it. It is very unlikely that an error in machining would have taken place to overbore the hole in the dipperstick. However, if there is a bushing in the dipperstick, That could have been left out during asssembly.
I have hooked an outer bucket tooth under a rock buried 5' underground in a trench and repeatadly stalled the hydraulics in an effort to pry it loose. I have also used the side of the bucket and the swing to sweep fill away from and into the trench I was digging. Both of these actions would place twisting loads on the bucket and dipperstick. My BH75 has suffered no ill effects from this.

Can you recall if you ever stalled the hydraulics while applying swing and bucket curl at the same time? Pushing sideways on a stump is the same as sweeping fill into/away and should cause no ill effects reguardless of engine rpm. The force the backhoe can exert is determined by the setting of the relief valve. Engine rpm has no effect on pressure. The speed at which the implement operates is determined by the flow it recieves from the pump which, of course, is dependant on engine rpm. I normally run mine arould 1500-1800 rpm. Reving it up and using the swing to "take a wack at it" would be a bad idea and I'm sure you didn't do that. With a previous backhoe, while digging out roots, I have used the bucket curl and swing to pull the root free. Although I saw some flexure, there was no permanent bending. The BH75 is built much stronger than the Kelly hoe I had before.
Plese let everyone know what you find out about this. If it is the application of swing and curl at max pressure that causes the bending, it would be the second "mode" which operators of this model should avoid.

 

[rswyan]

I have also used the side of the bucket and the swing to sweep fill away from and into the trench I was digging. Both of these actions would place twisting loads on the bucket and dipperstick. My BH75 has suffered no ill effects from this.

Can you recall if you ever stalled the hydraulics while applying swing and bucket curl at the same time? Pushing sideways on a stump is the same as sweeping fill into/away and should cause no ill effects reguardless of engine rpm.

I dunno what the manual on your BH75 says, but the ops manual on my BH4690B specifically states to never use the bucket and swing circuit to backfill trenches or holes as it can destroy the backhoe.

Might be something that one can get away with on full-sized TLB's but apparently these smaller hoes can't handle it. Might want to recheck your manual to see if it has a similar warning.

 

[grizzjeeper]

Hehe... he is not a pit bull... he is a boxer I wouldnt dare own a pitbull.

As far as using the side to side action to fill, the pressure is so low that you couldnt do any damage.