My Grapple cylinder problem

[uphill]

I finally added a Dehnerwelding grapple, hoses and electric selenoid valve thing to my non-quick attach bucket and haven't been happier. I've seen this many times on TBN and many thanks to those who have done this in the past. Their posts were the only reason I could attempt anything like this and I couldn't have done this without them.

Now my problem.
The boys (my sons) used the tractor and was pushing on a tree with the bucket as they were cutting with a chainsaw and the tree began to lean against the bucket AND the fully open grapple. When the grapple is fully open, the cylinder is at it's shortest (sucked up position).
So the final deal, the cylinder was pressured shorter than it should be. Does that make sense? Well the grapple wouldn't work any more and everything seemed to be in an extremely binded condition although not bent or damaged.
So we finally beat one of the cylinder pins out of it's mounting bracket and that removed the pressure. Then I pulled the cylinder out just like you would do a shock absorber. It seemed to be ok, so I hooked everything back up normally and the grapple began to work again. The only noticable indication is the grapple seems to open a little bit more open than before (cylinder might suck up more than normally).
So what happened and why did the cylinder quit working. A little explanation would be welcome. Thanks again.

 

[3RRL]

IMO the cylinder has not changed, but more than likely the mounting points/brackets/bolts for the cylinder were bent back or tweaked up and back when the jaw was open. That could push the pivot so it is more in-line with the cylinder so it would be harder to push the jaw down. Could also be that the jaw is bent or tweaked back farther. Could even be the pivot pins are bent or even a bent cylinder rod, but I doubt that. If the jaw opens up a little more than before,does the jaw close as much as it used to? If not, that will tell that something is bent. But like I said, I doubt it's the cylinder that squished. Cylinder may have been jammed because of the tweak in the steel where it is mounted. When you pounded out the pivot pin, it might have relieved some tension.

 

[uphill]

Thanks 3RRL, I guess you're right. I used the grapple for hours today and everything worked as normal. I was worried I was fixing to have to buy a new cylinder. Guess I lucked up.

 

[MJPetersen]

Rob must be right and the grapple must have just been in a bind, but, what bothers me is that why it would not work before you knocked the pin out. Hydraulics have tremendous power and if you were able to drive the pin out then I am thinking that it should have been able to overcome the bind.

I have a possible theory without seeing pics The only thing that I can think is that the piston was pushed in to the extent that it covered the hydraulic extend port. Some hyd cylinders have a stop collar to keep that from happening, if yours has one on the rod see if it has moved. If that were the case you should put the stop back where it was or you will damage the seals pushing them past the port lip all the time. It would now open further because the piston can travel into the port area until it blocks/almost the port.

That not being the case then great--you can go back to work and it was a cheap lesson for the "boys."

Mike in Warsaw

 

[jinman]

My grapple can go "over-center" when the cylinder is fully retracted. It takes just a little push from brush or limbs to cause it. When it goes over-center, it is in a locked position. To prevent this, I just stop the cylinder a tiny bit before minimum. It's only happened once and there was no damage whatsoever. Your grapple may be the same design. I just removed the pin and reset the grapple when it happened.

 

[3RRL]

My grapple can go "over-center" when the cylinder is fully retracted. It takes just a little push from brush or limbs to cause it. When it goes over-center, it is in a locked position. To prevent this, I just stop the cylinder a tiny bit before minimum. It's only happened once and there was no damage whatsoever. Your grapple may be the same design. I just removed the pin and reset the grapple when it happened.

Exactly Jim,
That is the condition I was trying to describe (obviously a poor job of it) that could have happened if any of the mount points were bent/pushed back. The cylinder would now not have a great enough angle to push from, tilting or pivoting the jaw down. It would be straight in line or thereabouts, like trying to push the jaw "off" the pivot instead of pivoting it.
...At least that's what I think?
Never did get whether the jaws closed to the same point as before though. That would tell if there was bending involved or the piston shaft pushed back as MJ refers to.