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Discussion Starter #1 (Edited)
Dealing with an issue on our 1995 JD 6400. A little bit of background first...

Tractor was bought new in 1995 and about 5 years afterwards, we noticed the lift arms would fall overnight. No big deal as we rarely used the lift arms (tractor is and has always been a haying tractor), and they functioned fine as long as it was running. Condition got worse in recent years with the arms falling immediately after shutdown. Again, still not a deal breaker, but I began to suspect a failing valve or hard part. Fast forward to this past December and we lose total lift arm and SCV function immediately while lifting a round bale with the high lift spear. I pulled the end plate off the rockshaft valve and noticed a chunk of cast broken off inside....with a crack that looked like it had been growing over time (explaining everything above). So, I grab a good used rockshaft valve from Bootheel, and slap it on (reusing my known-good stepper motor).



So, now everything is working EXCEPT the lift arms will only move about 3" when you cycle the lift arm lever. Meaning, if you want to raise the arms from min to max, you would have to move the lever about a dozen times....with the arms jumping up about 3-4" each time you cycle the lever (move it from about midway to up, back to midway, back to up, etc....). Same thing applies for lowering. It will indeed raise a load, but it requires the cycling mentioned above. The SCVs also act kind of strange, having a greater pressure as you turn the steering. For instance, when raising the hay rake, if I turn the wheel while pulling on the SCV lever, it will raise faster than if not. Without steering input, it will raise slower....even stalling when trying to raise a heavy load via the SCV (e.g. disc mower, etc...). PowerQuad and PTO both operate flawlessly and the steering is fine for the most part.

If I use a screwdriver to operate the stepper motor directly, it will raise and lower as intended (though it does have a "shudder" through the screwdriver when doing so), so I suspect the motor is not centered or the HCU needs calibrating. I do not possess the performance monitor to do my own diagnostics, though I do have the full set of manuals (TM4523 & TM4524). Obviously, all filters have been changed and system flushed and refilled with J20C spec fluid to the correct fill height.

Anything I can do without purchasing the performance monitor or hauling it to my local Deere dealer?

Thanks in advance!
 

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it sounds like you have air in the system. This may be a stretch, but maybe air is getting in the feedback line and not stroking the pump correctly. This would explain why everything works better when you turn the wheel or move an SCV. It is properly stroking the pump and causing good flow.

I'm no expert on PFC hydraulics or anything, so that may be a long shot...
 

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Discussion Starter #3
it sounds like you have air in the system. This may be a stretch, but maybe air is getting in the feedback line and not stroking the pump correctly. This would explain why everything works better whn you turn the wheel or move an SCV. It is properly stroking the pump and causing good flow.

I'm no expert on PFC hydraulics or anything, so that may be a long shot...
I thought about that too, but the fact that it raises and lowers uninhibited when turning the stepper motor screw directly should rule out an airlocked system, I'd think. Also, I've cycled the lift arm cylinders through their entire range of motion 6-7 times. Based on past experience (replacing hyd hoses, cylinders, etc....), that much cycling should purge the system of air. Thoughts?
 

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I have no idea. Wheres Tx Jim when you need him?:laugh:
 
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I'm lurking in Coyote Flats BUT SORRY my knowledge of JD tractors built after '92 is very,very limited.:unknown: IMHO all those electronically controlled hyd functions are great until they ""malfunction"" then they become a nightmare!
 

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Does your TM tell how to center the stepper motor? Mine for 6x10 series, TM4574 does. Page 70-15-8

When replacing the rockshaft valve, maybe a load sensing disk(s) for the SCV(s) was not put in???

TM states system must be recalibrated after parts replacement.

jd110 might be able to help :dunno:
 

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Discussion Starter #7
Does your TM tell how to center the stepper motor? Mine for 6x10 series, TM4574 does. Page 70-15-8

When replacing the rockshaft valve, maybe a load sensing disk(s) for the SCV(s) was not put in???

TM states system must be recalibrated after parts replacement.

jd110 might be able to help :dunno:
It does....section 270-15-61, but it requires use of the Performance Monitor as ours doesn't have the DG+ dash. Guess I'm gonna have to grab the monitor and cable to do this job. Was trying to satisfy the frugal part of my personality, but oh well.
 

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Discussion Starter #8
Small update....

Spoke to a buddy who works at a Deere dealer and he said they have an excellent old school service tech who has been around since the early 90's. I picked his brain for a bit and he's got me set-up with a procedure to manually center the stepper motor and check the screw depth of the raise & lower valves. I'm gonna tackle this tomorrow if we get rain. If not, I'll jump on it Friday and report back. Feel free to throw other ideas around in the meantime and if anyone has an RE39569 performance monitor they wanna rent out, LMK. :lol:
 
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