3PT shake and gannon attachment will not stay up.

I have a TO20 but as far as the year goes its unknown, when I engage the rear 3PT to lift the rear gannon attachment up it lifts and works just fine but I noticed if its lifted up to the farthest position up it shakes a little or bounces. Plus it will not hold the gannon in an up position for very long, it will slowly come down. Is the pump going out or are there some seals that will need be replaced...if so were do I get the diagrams to help me remove the pump and the parts needed to fix whatever it is thats not working.

Sounds like the Master Control Valve on your pump. Does it have good strength with the tractor running.? How quickly does it drop. The rule of thumb is if it takes more than 30 minutes to drop, leave it alone. If it drops quickly (a few seconds) like mine it is probably the Master Control valve. The Valve ususlly costs about $25 - $35 if you can put it in. If you have a shop do it you are looking at $400 - $500. I have replacement instructions if you like e-mail me and I'll send them to you. Good luck Joe