I have a JD3720 with the 300CX loader. I was moving some sand and while working the bucket started to gradually dump on its own. First it just would creep slightly then it got so bad that as I would drive forward and curl the bucket up it would fight being curled up. I would have to hold the control lever to the up position and not let it go to the neutral position. So I stopped and shut the machine down to pull the quick dis-connects for the hydraulic hoses apart. I found the red one which is part of the cylinders that curl up/dump the bucket, had an O-ring stuck in both the male and female quick dis-connects. I used a pair of tiny needle-nose pliers and pulled the stuck O-ring which split/broke. I then re-connected the quick disconnects back together because I was not sure if the o-ring came from them. The quick dis-connects are fine and the problem still is there with the loader wanting to dump on its own. I called local dealer, mechanic said that I probabley broke a cylinder rod and the o-ring came from the cylinder and got into the hydraulic line. Niether cylinder is leaking and they both move back and forth. Does it sound like a rod would have broke? Any ideas would be greatly appreciated.
Can you piece the old O ring together to define how big it was? I'm not sure how the cylinder rod is sealed to the piston inside the cylinders, perhaps it came from under the cylinder piston nut and now the fluid is leaking between the rod and the inside bore of the piston?? Another thought, did you switch the hose connectors from the boom cylinders to the bucket cylindrs to make sure sometning is not wrong with the control valves? Frank.
I did not switch the connections to the boom,but I could try that tonight. The mechanic at the dealer said that the oil is probably leaking by the rod and piston internally. I did piece the o-ring together. I did not measure it but estimate it anywhere from 1.5 to 2 inches. Which easily could be about the inside bore diameter of the cylinders.
I forgot to mention that upon inspection of the quick connects along with the o-ring was a tiny speck of yellow hard plastic. The mechanic said that is probably from the piston or rod wiper.
The size O ring you describe would be about the right size to have been on the outside of the piston. If that O ring was gone the fluid would get past the piston pretty fast. Being the line from the connectors goes into a "T" between the two bucket cylinders the fluid you are pushing thru to maintain curl would all go to the cylinder with the leaky O ring without affecting the opposite cylinder.
If all of these assumptions are corrrect I wouldn't use the cylinder too much for fear of the bare piston scoring the inside wall of the cylinder.
Let us know what you find.
Frank.
Well I hooked the bucket hydraulic lines go to where the boom up/down lines for the loader are suppose to be and the problem was still the same, the bucket wanted to dump.
So next I took the quick attach bucket off to operate the tilt/curl circuit of the hydraulics. This would let the cylinders operate more independant of each other, other than they are tied together by the hydraulic lines. I then operated the tilt/curl circuit and the left cylinder seemed to creep and the right one wanted to stay where I operated the tilt/curl. I then shut the machine off and pushed and pulled on each cylinder rod and the left one I could push/pull slightly and the right one would not budge. So I removed the left cylinder but have not had time to tear it apart to inspect it internally.
I couldn't figure out how to pull cylinder apart,niether could the dealers mechanic at first. Had to order the rebuild kit which came with a detaining ring to get the rod out of the barrel. The 1.5 inch O-ring and some other rings and wiper were chewed up. Also the nut was almost off the threads of the rod. The mechanic thinks the loose nut is what caused the problems. Put it back on the loader and problem is solved. It must have been a Monday or Friday at the John Deere factory.
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10-23-2009, 09:11 
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