i have a 770 motor grader that the right side blade lift cylinder will not stop moving in the up or down position after the lever is turned loose in the cab, to stop it you must tap the lever back to the center then the blade will stop. when you move the actual lever on the valve body on the right side blade it will not spring back like the left side lever will. John deere is saying that you can't rebuild the poppet valves on the 770 only later models you could, they say you must buy a complete valve section for that function. Does this sound right to anybody who has worked on one?
Gearhead75, Seeings how you said your machine has blade lift poppet valves I assume it is a straight 770 or 770A. When I lived in southeast Colorado there was still several counties that had these machines. I rebuilt plenty of poppet valves during that time. Most of the time installed new seals and maybe some pressure or return seats. Need a couple of special tools to install hog rings and to seat the valve back into the blade control valve body. Your dealer may not have the tooling or anybody old enough to remember how to rebuild them. I would look at JD parts online and see if the reseal kits are still available. Good luck,
coalrulz, Do you remember what came in a rebuild kit, was it just o-rings or were there any hard parts. What fails in the valve, your right in that no one knows much bout them and it is a straight 770.
Gearhead75, There was just orings, backup rings, and hog rings. If you need any of the pressure or return seats, or any other parts they have to be ordered seperately. If I recall correctly Deere used to offer a complete poppet assembly. But remember there are two for each function, blade lift (each side). Hope this helps.
sound like a spool valve problem. . getting stuck.
Having same problem with a jd77A motor grader in Kenya. I have dismantled the poppet valve and the seals are worn out including the rings. Want to import the repair kit. I need to contacts for a dealer.
I had an issue similar to that on my 772 BH but it was the articulation function. I replaced the O-rings in the poppet valves under the cab and that was the solution.