Backhoe M59 hydralic saftey?

[wdchyd]

Looking at the workshop manual I can see it now. In fact, Kubota mentions the cushion design several times and goes into some explanation for how it works but without any detail as to clearances and such. From their section drawings it looks as though they have figured out how to make the configuration of the rod&piston part of the boom cylinder in such a way that it causes the flow of hydraulic oil to be restricted at the ends of the stroke. That would explain why the boom slows down so much just before latching.
The swing cylinders are made the same way, but not the dipper, bucket, or thumb cylinders. The thumb cylinder could benefit from the same technique. It tends to crash at the end of it's stroke and I don't see any advantage to its doing so.

Interestingly, the parts manual only covers the tractor itself. I'll have to check with Messick (from whom I get my manuals) and see if Kubota has printed the parts manuals for the backhoe and loader yet.
rScotty - M59

Most of your "High End Mfgs" do this routinely, simple hyd cyls do not have cushions in them due to manufacturing costs.....they are common in heavy equipment....the only time you'll see them in small equipment is if it does damage at end of stroke

 

[KubotaTech]

There is a service bulletin, I had replaced one for this problem, even with the new cylinder it slows down at the end of the stroke, but does fully return.

 

[rScotty]

Most of your "High End Mfgs" do this routinely, simple hyd cyls do not have cushions in them due to manufacturing costs.....they are common in heavy equipment....the only time you'll see them in small equipment is if it does damage at end of stroke

I agree that you don't see hydraulic cylinder braking all that often. But I wonder if the reason really is manufacturing costs? I think we tend to think of cost as the reason for more things than it is. Competence, advertising value, and just plain accident dictate more designs than we admit to. I design a lot of parts, and have a pretty good idea of what different configurations on the same part will cost. It seems to me that it's necessary to machine the end of the cylinder to some shape, and the actual shape doesn't much matter since it's just an automatic program.
Kubota didn't put in hydraulic braking in some places and not others for bragging rights - we know that since Kubota doesn't even mention it in their advertising.
Could it be that the difference is simply the difference in the competence of two different Kubota hydraulic cylinder designers? Maybe the old master and the apprentice? You see that happen a lot in other mechanical designs.
rScotty

 

[SB photo]

There is a service bulletin, I had replaced one for this problem, even with the new cylinder it slows down at the end of the stroke, but does fully return.

even with the "updated cylinder" it seems to be doing it again any thought?

 

[rScotty]

even with the "updated cylinder" it seems to be doing it again any thought?

Exactly what is it that it is doing? Is the cylinder retraction slowing down to a crawl at the end of the stroke while at the same time the motor labors? That is how they are designed to work. Does the cylinder have enough movement to return far enough so that you can work the manual latch? In other words, can you get it to latch?

I'm thinking that if two cylinders do the same thing, it is time to look to something else. In this case that would be the latch. Possibly the latch itself is not made to the right dimensions. That is where I'd check next. Mine was very difficult to latch and unlatch until it developed a little wear. Just measured mine, and when the boom is fully retracted, there is approximently 0.120" of clearance between the large pin and the claw of the latch with the boom fully retracted and the latch in the engaged position. During that last 1/8" movement the motor labors and the boom moves quite slowly. Then the clearance from latch jaw to pin goes to zero as the pressure in the boom relaxes and the latch comes fully into play. In that engaged position the arms of the latch are about .050" above the square stops that limit the downward latch movement. I have to retract the boom again to regain the clearance in order to unlatch it before using the backhoe.

Initially I was surprised by the tight clearance. Because the movement of the latch jaws is a a portion of a rotation rather than a straight line translation, the 0.120" clearance is just barely enough clearance for the jaws to clear as they rotate in order to latch and unlatch the boom. When new the clearance was even less, and the large hand lever needed more of a shove than could be fully accounted for by the resistance of the safety retaining spring alone. After a few hundred hours the hand lever is only resisted by the spring. Given the large pieces of metal involved and the multiplicity of geometries that have to be just right for it to latch, Kubota designed it pretty tightly. All manufactured parts have a range of tolerances and I wonder if your various tolerances stack up so that the latch claw is a little too short - making it too tight? As manufactured, the tolerances are smaller than I would have expected.

It would seem a minor matter to get the exact cylinder specifications from Kubota, disconnect the cylinder at one end, and then activate the cylinder. Measure the open and closed lengths. Note if it slows down properly. That would tell for sure if the cylinder is the problem or if we should be looking elsewhere.
rScotty.

 

[SB photo]

I looked at what you are describing thinking that same thing maybe something moved or any possibility that didn't look right, jumped on it today and it works better than ever the only thing that was different was the hydraulics where warm normal temp, not hot when the problem occurred and even when I had the problem I cycled the cylinder a couple of time and it did latch with just a little more force than usual I will keep you posted if anything else develops. And yes the machine had very tight tolerances.

 

[rScotty]

I looked at what you are describing thinking that same thing..........works better than ever the only thing that was different was the hydraulics where warm normal temp, not hot when the problem occurred............ and even when I had the problem I cycled the cylinder a couple of time and it did latch

Hmm...I think you may have hit on it. Hope we remember to check back with one another in a while and see how it's going when the M59 has some more hours on it. Normal expansion with heat coupled with an unusually tight clearance during manufacture could easily explain the whole thing. I hope so, because if that is so it will probably "wear in" and be just fine.
rScotty