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!