3 point wont go all the way down

[yomax4]

Hi Smarter than me folks.. I have an Iseki TA247 which is a Massey 1240/1250. I can raise my 3 pt just fine but it suddenly doesn't want to go down only half way. Then while its sitting there it will jerk down an inch, then another, then may stay up until morning when I see it went down with tractor not running. I searched all over the forums and couldn't come up with a cure so I'm begging for help. This tractor does have the box next to the seat to control draft, speed to lift and lower and a knob that adjusts how high or low the 3 pt goes. I turn the knob all the down and it still wont go down. Tomorrow I could go out and it would work perfect for an hour or 2 and then start to act up. Any ideas would be appreciated. Thanks.