I have a 1977 Ford 3600 that won't maintain position when using anything on the lower arms. It will raise and lower without a problem even with a heavy load but you have to have it all the way up or on the ground. If I want the link box to maintain a height (say 12 " off the ground) it will gently fall back down.
If I try to reverse into a pile of stones, the link box will just ride up over them.
The Draft/Position lever is working OK. I've even taken the Hydraulic Lid off and taken it to my local Ford dealer. They said a pin in it was heavily worn and was replaced, they also replaced all the O rings then set it up on a rig. However it didn't really make any difference.
This causes real problems when using the pick-up hitch with a trailer as the arms drop and get caught on the trailer draw bar when turning corners.
Can anybody help. My head's pickled and the Ford guys just shrug their shoulders now.