D17. What is this?

I am trying to troubleshoot my lift system when I found this arm. There is no linkage hooked to it. I removed the round cover on the side of the case and the arm definitely does engage a gear. What does it do and should it be hooked up? Thanks. 

Edited by robescc - 26 May 2016 at 1:08am

^^^ That's how mine is.

What went wrong with the lift? Inside the cover you have at the bottom of that photo is the piston pump. They are know to get plugged up with gunk you will want to clean it up good before you reinstall it.
How is the oil in the transmission? There is a hose that runs through the rearend that can go bad and will overfill the transmission with the hydraulic oil from your lift system it is the supply line to the cylinder.   
There could also be something up with the Draft control system but before anyone can give advice on that we would really need to know what was the original issue.

Hydraulic fluid is the correct weight. 20 weight oil. Not sure what the issue would ne with lighter oil. Sounds like a problem with the traction boost setup or adjustments. Looking that up in the service manual would be a good place to start. Up and won't come down is usually the traction boost because it takes oil pressure to raise it. Also how much counter weight do you have on the hitch it will probably take about 200 pounds of weight to get the arms to come down as it is gravity down.   With the tractor powered down and the levers set to lower the lift you should be able to put weight on the lift and see it fall which will prove that the plumbing is not plugged up. I suspect it is either a lack of weight or the traction boost system. I don't know the traction boost well enough to tell you how to fix it but doc or Mac would know what you should look at.

loosen pressure line at the back and see if it relieves the oil and arms come down... while the tractor is off.  Might have seals going bad in cylinder, or hose having rubber come lose inside and plugging line.