LS MT357 Stuck Speed Control Valve

[CowCreekFarm]

I was using my LS MT357 to grade the driveway. I lifted my driveway grader to turn around. When I went to lower it. It would not go down. I assumed it was the speed control valve. So I tried to open it. The knob would not turn in either direction. I figured the linkage from the knob to the valve was binding. So I removed the seat to get to the linkage. Once I disconnected the linkage from the valve. The knob and linkage moves freely. So I tried turning the shaft coming out of the valve. It will not move in either direction.

Any ideas on what could be causing this?
Is there a way to relieve the pressure before breaking loose the nuts on the valve and making a mess?
Dealer says he has never heard of this...

 

[ptsg]

Lack of use will eventually lead to seized valve as the rust around the shaft does its job.

You can loosen that nut but do it slowly, because there is fluid under a decent amount of pressure behind. You want to let it leak down as the 3 pt drops, eventually, it will drop all the way and there is no longer pressure behind it. Yes, it will make a mess by the way and don't get in the way of the implement dropping so you don't hurt yourself.

Then, you can pull the rest of the nut and shaft out to inspect, clean and hopefully get it to spin again. Be careful as there may or may not be some small parts inside it. Make sure you don't lose those and you note the position of those as well.

 

[Avenger]

Could be debris in the speed control valve as well. I think it mess time. Get the implement on the ground, relieve the pressure, and take things apart.

 

[CowCreekFarm]

Now I have that broke loose. I don't think that was the problem. Looks like someone had opened the speed control valve aggressively open from the factory. Since I had never moved it. It just stayed that way.

But now I start the tractor up with the lever in the down position for the 3 point and it lifts the implement?????

 

[GS650GL]

There is a spool stuck in the hitch control valve if it wants to raise with the lever in the down position. It probably raised all the way up and didn't cancel out, so it was still trying to raise when it can't go any higher. That builds pressure on the drop speed valve so you can't turn it. You have to lower the hitch to relieve the pressure, but you can't because it won't lower, so you're screwed. Saw this happen twice. The hitch control valve under the lift cover will have to come out to fix it.