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Discussion Starter #1
Suddenly while clearing snow my loader bucket roll control has gone essentially dead, boom lift and third function (4-in-1 bucket) are unaffected. No fluid leaking anywhere, and if I manipulate the bucket to a roll position when holding the control open it will stay there when I release the control, which leads me to believe it not a cylinder problem. But it does not respond to commands for either "close" or "open", it just goes "limp". I have always suspected this control valve was not just right as it would not hold the bucket roll position when down pressure was also applied, but I dismissed this as a safety feature to prevent machine overload. I hope my SCV is not totally gone, it's a very expensive part. The parts diagram I found online does not show any parts breakdown for the valve, are individual valve parts available? Any other thoughts beyond checking all linkages once I can get it into my shop would be appreciated? Thanks,

gephet
 

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There is usually not much to go wrong with the scv. The only parts replaceable are the orings. They leak externally when they go bad. Does your control lever feel normal? Does it spring back to the "neutral" position? If so, then I suspect you probably have a cylinder problem. Try tying the control lever in position to curl the bucket back for maybe 5 minutes. Feel both bucket cylinders and see if one is warmer than the other. If oil is bypassing in the cylinder, it should create heat. Get a reseal kit for the one that is warmer.
 

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First of all..
2442877


second...let me ask you to stop in at our Introductions forum Introductions and tell us a little about yourself and the equipment you have,,,then you may get some more response at Hydraulics our hydraulics forum...some real wizzes at this subject...someone who can help you will happen along and chime in
 

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Discussion Starter #4
jd110:

Thanks and I will try your suggested test. It seems to me that if one of the cylinders were bad I would not be able to lock the bucket in any curl position at all, but I will try that test. Yes, the control lever feels normal.

Mark:

Thanks for the welcome. I really did not find the forums that easy to navigate that I found the "Introductions" section. I will try to look that up at some future point. I'm a 12 year owner of the machine at question here, a former owner of a a 3400(?) CUT, a 25+ year owner of a JD 350 crawler-loader, an experienced mechanic, and mechanical engineer.
 

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Discussion Starter #5
I came up with an easy way to determine if it was the control valve of the hydraulic cylinders. I simply switched the positions where the hydraulic lines from the control valve plug into the loader assembly so it can be removed. Despite what I was thinking was a SCV failure, this proved that to be wrong. It had to be a bucket curl cylinder and jd110's procedure to identify which cylinder worked perfectly, thanks much.

I got the parts from my local dealer. Turns out the piston retaining nut had come off the ram, and the way the cylinder behaved is what cause me diagnostic issues as in one direction the piston was being pushed back onto the ram and it worked much like normal. I was very lucky it did not cause any real damage and just the two seal kits (~$65) fixed it. The design of the JD hydraulic cylinders is poor from both a serviceability and durability standpoint IMHO. They are a pain to dissemble and a big pain to reassemble. My task was made more difficult by the fact that the piston had come off so the ram just fell out leaving me with nothing to pull the cylinder end cap with or get the piston out with. I'm glad I watched a couple online video's before I started and had a variety of pullers, one which I was able to dissemble, position, then reassemble and use to pull the end cap.
 
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