JD 570A Saddle pins

[rsherril]

I have decided to repair or replace a saddle pin cylinder on my John Deere 570A grader. We determined that the pin wasn't frozen in place when we were able to get it to retract with the aid of an air hammer while the saddle pin valve was depressed, (open).

Examining the technical manual I learned that the saddle pins are in a parallel circuit, (there are two of them), and are suppose to disengage, (retract), when the saddle pin valve is opened. At first try, both took some assist with the air hammer to disengage. Then when the saddle pin valve was closed, both pins returned to the engaged positions with no assistance. Repeating the procedure, only one pin would return to the disengage position even though both pin holes had been cleaned and coated with never-seize. The air hammer pushed the remaining pin in to the disengaged position, but it would not go on its own without the assist.

The technical manual tells me that on retraction there is a difference in pressure on each side of the piston forcing the pins to disengage. When the saddle pin valve is released "the check ball seats in the return passage of the saddle locking valve. Due to the orifice slot in the piston seal ring, pressure on each side of the piston equalizes. The difference in areas on each side of the piston forces the locking pin to engage". This is a little confusing, but I'll guess that is where that orifice slot comes in, sort of a controlled leak back.

Questions: What is this type of hydraulic cylinder called? Single action?, Clevis pin ? ???

John Deere sells all the parts to build a new one, but not a rebuild kit or rebuilt cylinders so is it standard operating procedure for owner operators to do the rebuild? (Service records indicate that the functioning cylinder was rebuilt on site about twenty years ago at a paving project.)

Any suggestions or advice will be welcome. I've included the page from the TM for the Saddle Pin for reference.

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[Cmark]

I'm not at all familiar with your machine but the circuit in the book is quite straightforward. My guess is that your piston seal item 12 is leaking. It only comes into play when the pin is retracting.

 

[AndrewC]

According to the parts pic Im looking at your ring should be 9. I suspect your parts guy is looking in the old s/n break. I dont see deere doing something like you suggested. If anyone had done it, it would be the last guy. See if this looks right to you.

 

[rsherril]

From my trip to OZ today I learned that the saddle pin piston seals are a stress point because some of the energy from the blade is finally dissipated into the barrel cylinder there, causing it to wallow out over time, (these machines are at least twenty-five years old). So the barrel cylinder seal is out of tolerance where the retract cycle starts and back in tolerance about 1.5 inches down the tube. This explains why it won't retract, but has no problem returning.

The factory piston ring seal is not designed to take up the difference and hydraulic pressure is dissipating through the gap at the start of the cycle. A new piston seal ring of the same design will not solve the problem. The service department solution was rather complicated and expensive so I ended up at a hydraulic speciality store.

Their solution is a side seal piston ring which can adjust to the differences, so I ordered one with high hopes. We shall see.

 

[rsherril]

Update, the saddle pin cylinder is back in place with the new "hydro seal piston ring". All systems go. My cost is $12 plus two trips to town and a couple of hours wrenching. I'm glad that the dealer's parts man sent me to the hydraulic shop. Now I can really stress that old grader out.

AndrewC your parts diagram matches mine, the confusion was there are two rings, one piston and one barrel (#9 and #16) and both are just labeled "ring". Parts 12 and 13 are nowhere to be found in my cylinder. Like you say I have no idea who worked on it before, so they might have been left out by the other guy.

Thanks for the help and I hope that my experience can be used by others.