Grapple Attachment Tie Rod Hydraulic Cylinder Questions

[BillP2]

Hydraulics newby here. Repeat, newby alert.

Have a used grapple Armstrong attachment which has two 3" bore by 8" ASAE stroke tie rod cylinders. The rod ends are 1.25", and the clevises are threaded.

Grapple manufacturer installed Maxim cylinders. Back in the day and before my time, one started leaking, so prior owner replaced both of the Maxim cylinders with new Cross cylinders. I still have both Maxim cylinders.

This weekend, one of the Cross rod-end clevises snapped. I can thread on the Maxim clevis, but it is threaded slightly "shorter" than the Cross clevis.

I showed this to an experienced neighboring farmer, and he said that grapple would not work correctly with one Cross Mfg clevis and one Maxim clevis because of the 1/4-3/8" difference in how far the rod-end screws into the respective clevises.

I then asked how one got each cylinder connected so that they had same stroke amount while "at rest", and before firing up the tractor. He said to disconnect hoses on the broken clevis cylinder (after de-pressurizing system), then manually pull/push so that I could get the clevis at re-attached, and then when I powered the system would equalize. I wasn't thinking fast enough to ask, "well why won't it compensate for the 1/4-3/8" difference in clevis thread?"

That leaves at least two questions:
1. Is it any problem to install Maxim rod-end clevises on both of the Cross cylinders?
2. How do you get each cylinder connected so that the have the same stroke amount?

Thanks in advance,
Bill

 

[K5lwq]

What caused the Cross cylinder to fail? I think I would rebuild the Maxim cylinders and put it back original.

 

[Vigo327]

Ok, first off, how much thread engagement do you have? Are you screwing it on until it stops? It's possible that you have more thread engaged in there than you actually need for strength (it isn't the threads that broke here, is it..) in which case you would just unscrew the thing until the cylinders' extended and retracted lengths matched. BUT that's assuming that a: there would still be enough thread engagement, b: the threaded yoke has some sort of pinch clamp or something to keep the rod from gradually unthreading itself out of it during use, and c: that the cylinders' strokes are actually the same in the first place. But if those 3 things are all true, it would be the easiest solution.

As far as getting the cylinders to be in the same place for hookup, it's very easy.. with the rod ends unhooked, the cylinders will NOT usually move in sync. Usually one will have less resistance to movement than the other one, so that one will move first until it is all the way extended or retracted, at which point the other one will start to move. BUT you can easily make both cylinders either extend all the way, or retract all the way by just holding the lever until they both hit their limit in that direction. So you just need to find a way/angle to hook up the grapple lid with the cylinders either fully extended or fully retracted because that is the no-effort way to 'sync' the cylinders without unhooking anything.

As for why it won't compensate for a slight length difference in the cylinders, it actually will.. UNTIL one of the cylinders runs out of travel and the other one keeps pushing. That will put a good twist on whatever is hooked in between them. Best case it just wears your pivots out early. Medium-bad case, it fatigues the metal and causes something somewhere to crack after repeated flexing. Speaking of which.. mind posting a pic of the broken clevis? Just looking for underlying issues which might make the thing break again in the future.. And worst case is it puts a permanent bend evenly across the whole thing.. which is very finicky to impossible to precisely unbend, after which point your pivot points will forever be misaligned and wearing excessively and god help you if you ever drive the pins out and have to somehow get them both back into their crooked misaligned holes.. So it is critical that the two cylinders sharing one grapple lid stop in the same places on extension and retraction.

 

[BillP2]

What caused the Cross cylinder to fail? I think I would rebuild the Maxim cylinders and put it back original.

I wasn't running it. Operator said that one of the R clips was missing on the rod end pin, so the pin worked loose, started coming out, and put uneven stress on the rod-end clevis.

As to Maxim rebuild, I tend to agree. The Maxim clevis are much hurkier/hercier than the Cross clevis. Sad, because Cross say "made in USA", which I would like to support.

Thanks for reply.

 

[BillP2]

Ok, first off, how much thread engagement do you have? Are you screwing it on until it stops? It's possible that you have more thread engaged in there than you actually need for strength (it isn't the threads that broke here, is it..) in which case you would just unscrew the thing until the cylinders' extended and retracted lengths matched. BUT that's assuming that a: there would still be enough thread engagement, b: the threaded yoke has some sort of pinch clamp or something to keep the rod from gradually unthreading itself out of it during use, and c: that the cylinders' strokes are actually the same in the first place. But if those 3 things are all true, it would be the easiest solution.

There is plenty of thread engagement, and yes both the Cross clevis and Maxim clevis each have pinch clamps. So, it is simply a matter of ensuring that the "control end pin to rod end pin lengths" are the same for both cylinders, regardless of manufacturer. I understand now per your third paragraph below.

As far as getting the cylinders to be in the same place for hookup, it's very easy.. with the rod ends unhooked, the cylinders will NOT usually move in sync. Usually one will have less resistance to movement than the other one, so that one will move first until it is all the way extended or retracted, at which point the other one will start to move. BUT you can easily make both cylinders either extend all the way, or retract all the way by just holding the lever until they both hit their limit in that direction. So you just need to find a way/angle to hook up the grapple lid with the cylinders either fully extended or fully retracted because that is the no-effort way to 'sync' the cylinders without unhooking anything.

Makes sense, although the "...find a way/angle to hook up the grapple lid..." may be interesting.

As for why it won't compensate for a slight length difference in the cylinders, it actually will.. UNTIL one of the cylinders runs out of travel and the other one keeps pushing. That will put a good twist on whatever is hooked in between them. Best case it just wears your pivots out early. Medium-bad case, it fatigues the metal and causes something somewhere to crack after repeated flexing. Speaking of which.. mind posting a pic of the broken clevis? Just looking for underlying issues which might make the thing break again in the future.. And worst case is it puts a permanent bend evenly across the whole thing.. which is very finicky to impossible to precisely unbend, after which point your pivot points will forever be misaligned and wearing excessively and god help you if you ever drive the pins out and have to somehow get them both back into their crooked misaligned holes.. So it is critical that the two cylinders sharing one grapple lid stop in the same places on extension and retraction.

Don't have the broken clevis with me, but cause of breakage was missing R clip on the rod end clevis pin. Pin started working its way out, putting uneven stresses on clevis, leading to breakage.

I now understand how critical it is that the fully retracted and fully extended lengths, measured center of pin to pin, be the same for both cylinders. This makes too much perfectly obvious sense, at least after you explain it. Like the Doug Stone country western song from the 90's, "Why didn't I think of that?"

Thank you.

 

[Vigo327]

Glad to hear the breakage is such a simple 'smoking gun' case.. if it were more complicated i'd be worried about what i'm missing and not be able to enjoy the use of the thing so much until i forgot and got over it.

As far as finding a way, I would expect that with the cylinders fully extended and the grapple lid sitting closed just due to gravity, it would already be fairly close to being aligned. If the grapple lid needs to go up, that would probably be pretty easy with a floor jack, or long prybar/jack handle/2x4 for leverage. Definitely easiest with a 2nd person to stab the pin while you control the grapple lid since it's probably a game of Twister to reach both things at the same time. Often times i hate to ask for help because i don't want to have to try to explain what needs done..Good thing here is a helper won't need much edumacatin' beforehand on how to insert a pin in a hole..

 

[BillP2]

Thank you sir!

Is there any reason I couldn't mount the two Maxim rod-end clevises on the two Cross cylinders, again, as long as distance pin-to-pin on both sides are equal?

Hopefully this would work until I can rebuild that one leaking Maxim cylinder.

 

[Vigo327]

Yes, should work fine.

 

[BillP2]

I thought it should, but needed a knowledgeable opinion. Thanks.

 

[LD1]

Yes I would replace both clevis's.

But even a slight difference in length shouldnt matter much as long as the cylinder bores are the same....they are pushing with the same amount of force.

Is there a mechanical stop? IE....when lid closes tight or opens all the way, is it actually out of cylinder travel? Cause if not it wont matter