I recently picked up an 1850.  The lift arms will not drop.  After the tractor has set a day, the pressure bleeds off and the fall as they should.  As soon as you start it, they raise to the full up position.  This has to be a relieve valve issue.  Adjusted the threaded rod for the linkage all the way in and no change.  (Yes the rock shaft arm is all the way forward). I have all the manuals, they talk about a fuzzing noise, I do have that as well I think.  The last guy never used the lift arms and didn't even have the arms or linkage anymore.  I'm wondering if he adjusted the relieve valve to keep the arms up.  There is also no free motion at the top they refer to, suppose to be 1/2-1 inch.  I could understand if it didn't go up.  I'm gradually going thru the tractor and making everything as it should be so I haven't used it at all yet to know what kind pressure I have at the remotes.  Need to go get a gage I guess and check it at the port on the side of the case.

As soon as you move a control lever for a remote, the fuzzing noise stops by the way.