I own a 96 john deere 690elc ex with hyd thumb. This machene keeps breaking the rod (chrome part ) of the bucket cyl. I dont have alot of slop in my bucket. The pin brackets that the cyl mounts to are square as to be expected. Is there suppose to be some kind of motion stop on the forward and back of the bucket that is flexing this rod. Or do i have some type of relief valve not working right . They break in the center of the rod . Ive been in this buisness all my life ran all types of equip and not seen this happen before. This 690 has done it twice to me and Im runnning out of patients and money. About 8 months passed beween breaks approx 250 hrs put on machene between the breaks. PLEASE HELP. THANK YOU!!!!! JOHNNY
A couple of questions first. New operator on the machine recently..? Genuine JD rods or "will fit" from some hydraulic shop or other..? If the rods were used then how much do you know about their previous life ..? Just trying to rule out the possibility of incorrect operation, wrong or weak material. Can you post a pic showing a close up of the fracture face of the rod..? Either side of the break is fine. I suspect it could have something to do with your thumb installation. First thing I would be checking is the line relief valves in the bucket cylinder and the thumb circuits, that's if the thumb circuit has one.
I'm with nige, check and make sure that the thumb reliefs and the curl reliefs are at specs. Its possible that a previous owner turned up the curl circuit, as well as the relief being way high on the thumb.
No new operator havent owned the machene but a year or so. It came from colorado so the first one i thought it may just be metal fatigue. The 2nd cylinder was from a parts house that has done me right in the past. I bought the complete cyl and they claimed it came off a john deere machene. Then they repacked it for me and inspected it came with 90 day guarantee. I called them and they stood by what they said as the truth but couldnt say for sure the rod had never been changed. Working on a big bid for next couple of days. I will try to get a picture. The break itself is in the center of the rod. No bend just break at a 45* angle . No sign of cracks before hand in the break. No discoleration just 45* angle riged rough break. THANK YOU ONCE AGAIN FOR YOUR HARD EARNED KNOWLEDGE. P.S. MY SPELLING SUCKS
ok, so did you check the thumb pressures?
Stump jumper It will be A few days. Im bidding on a demolition job that includes 118 houses and the city isnt making it any easier. I appreciate the help but I will have to get back with you in a few days. THANK YOU JOHNNY
I have been told that older cylinder rods build stress over time and that cracks can occur and propagate underneath the chrome. Examining the fracture site would tell you if it was a progressive failure. You would see what are called beach marks. These marks basically match the marks you see on a sandy ocean beach as the tide is going out. I have only seen rods bent and that is usually from hitting or being hit by an external source. I have seen the eyes broken off the ends of the cylinder rods but I figured those had to do with the welding procedure used to install the eye in the first place. Good Luck!
When I got out of college before getting back to being an operator I worked as a machinist at a shop that built custom cylinders. Ive seen a few broken on excavator buckets from popping mud out of them. Most cylinders on hoes have cushioning valves in the cylinders except the bucket on alot of them dont to help pop them. When the bucket pops it will cause the bucket to pull onn the rod from the shock. If it was from the thumb relif being too high the rod would be broken from a bend from compression. If you can post a few pics of the break and the ends of the breaks. Also were the breaks shiny on the ends or kinda rusty part of the way through like it hade been crakked a while. I take the parts place supplied the whole cylinder for the machine. I think the cheapest way out and safest thing would be to have a new rod made spec at a reputable hydraulic shop.
Agreed. That's why we need photos as I mentioned above.