Tractor Repair: sinking hydraulics, brush hog, hook ups

Question
I have a John Deere 4400 utility tractor with a brush hog attached to the 3point hitch, I think around 2000 year. When the 3point hitch lever is moved up the brush hog does not raise until the lever is almost to the top of it's slot, then it seems to raise slow and when the brush hog reaches the fully raised position the motor starts to bog like it is still trying to raise the hitch. If you move the lever down a little the bogging stops but the brush hog will slowly sink until it is all the way down. It use to raise its self to maintain the brush hog mowing height, but now it will usually sink all the way down and if it does correct its self it raises higher then it was before. It also will lower fast if you are not careful it will slam to the ground. The hydro fluid is the original fluid, it use to drip from the front end loader hook ups, but hardly any drips now. Is the fluid bad? or is it a lever adjustment issue? or bads seals? I have worked on engines but never hydraulics, please help.

Answer
Hello,

   Anytime a hitch sounds like it is still trying to raise when it is already all the way up, there is some internal linkage problem.  The linkage that is supposed to follow the movement of the hitch to tell the hitch valve how high the hitch is, has either broken or came loose.  I work at a Case IH dealership, so I am not familiar with a John Deere 4400 hitch system and don't have access to any service manuals or parts breakdowns to give you exact details of how to fix it.  If the fluid is original from that many years ago, it definitely needs a fluid and filter change, but that's not going to fix your hitch problem.  The valve apparently isn't getting a hitch height signal so it doesn't know what to do.

                    Good luck,

                       Arnie