I have fought this issue since I first added my 3rd function 5 yrs ago or so on my first tractor (don't recall exactly when...) Everyone always chimes in with the same advice, which is apparently a common issue: The implement heated up and built pressure in the sun, or the tractor did, etc. This is not the case. I could disconnect the grapple on my 3rd function, then immediately try to reconnect it (using all proper procedures for pressure release, etc) and you could not do it. No sitting in the sun, or months to have pressures change, I mean within seconds. I finally cried uncle and built a reliever for myself. This is a few pipe fittings and a male coupler on one end, and a female coupler on the other end. I attached each coupler to a 3" or so pipe, and then put a 4-way "tee" fitting in the middle with a couple short pipes sticking out as handles (I left the handle out on one, and it worked fine too, FYI). NOTE - the handles are not capped, so this is open to the atmosphere. Push this onto any fitting that is fighting you and you will spit a little fluid into the pipe and it will now go together. I stuff a paper towel in there to soak up the fluid, and drain on occasion. This has been true now for 2 different tractors, so it is not me going insane, it is not the tractor, it is not the temperature differential, etc. These things just allow pressure to remain that will not allow you to re-connect without something to relieve it.
