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  1. #1
    Silver Member qstott's Avatar
    Join Date
    Jan 2006
    Elm City, NC
    '65 110 JD, 445 JD, 4720CabJD

    Default Rate of drop/lock valve adjustment on 4720

    It seems my adjustment knob on the drop/lock valve is not working correctly. When I first got the tractor in December with 761 hrs, the knob was hard to turn, almost impossible. I could see where the rod comes out from under the seat and enters the housing under the tractor floor. I sprayed rust penetrate at the point where the rod enters the housing. The knob will now rotate clockwise and counter clockwise, but doesn't seem to make any difference in the rate of drop. It acts like the rod is turning in the fitting. Anyone have this problem or suggestions? I hesitate to put a lot of force on the fitting to twist it. You think it's just frozen from lack of use? Thanks!

  2. #2
    Super Member greg_g's Avatar
    Join Date
    Dec 2003
    Western Kentucky
    JD3720 Cab, 300X loader with 4-in-1 bucket

    Default Re: Rate of drop/lock valve adjustment on 4720

    Mine is too new to have developed this problem yet, but I've fixed this on other tractors. What I found in the past is that it's binding due to rust. Hydraulic fluid is hygroscopic, meaning it attracts water. It must be changed periodically, just like brake fluid. If not, rust starts developing in the hydraulic system. One of the places is the needle valve that is behind that flow control knob.

    I had to remove the valve from the tractor, clean both the valve body and the valve seat, then reassemble. Also - on frozen valves - the knob can break loose from the valve stem. That will give you the false impression that the valve is turning, when it's actually only the knob that's spinning on the stem.

    USN (Ret)
    Former Chinese tractor owner (x4)
    Current John Deere owner

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