460 hydraulic problems.

My fast hitch hydraulic circuit has the original draft sensing valve removed and a conventional valve has been put back in it's place. The hydraulics load up bad when the engine is running, drag down the RPM's and blow the relief valve open (I assume). I have a short hydraulic hose connected to the inlet and outlet valve with the longest remote valve handle and it is pulled back with a rubber bungee. It helps some but there is still pressure in the system. If I raise or lower the hitch it goes away until it reaches the up or down limit of the hitch. It does not go away if I center the remote lever for the hitch. I bought this tractor with a bad TA and hydraulic pump. Both have been fixed and there is fresh hy-tran in the tractor but I'm sure there may be some garbage in the hydraulic system. Any ideas what's wrong? What I can't figure out is that if the large (or short) handle is held back all the pressure should be relieved on the system shouldn't it? Or is there a priority flow valve that still sends pressure to the hitch? If so, centering the lever on the hitch should take pressure off of the system I would think.

The Simi open center system has a pilot demand control valve (internal) and a tiny screen that is associated with it. If these are stuck, or plugged, it will be on "demand" at all times as you describe. It is simple to get at but requires sheet metal removal and getting into the valving. Jim

I've been doing some searching here since I posted. Are you talking about pulling the cast cover with the four bolts that faces your left ankle as you sit on the tractor? All my sheet metal is off.

Sounds typical for a system staying on demand . Like others suggested, make sure your single and double action setting on the aux valves are lined up, no bent or broken roll pins. If that checks out you will need to take the four bolt cover off regulator, relief valve assembly. Note, heavy spring under cover for relief valve so take out two corner bolts and put longer ones in to avoid things flying apart. You will find a screwdriver head orfice with screen . Depending on how many times it has been repaired over the years, the original had a roll pin through the orfice holding a check ball in place. This check ball bounces back and forth and closes the orfice down. As this is a hardend seat they are difficult to re drill to proper size but can be done. It is only .031 so you need wire gauge drills to do so. Screen most likely is collapsed and plugged, you can cut off bottom to clean and wrap it back up again if it is not broken. Now for the fun part. Sometimes you have to make the hole in orfice slightly larger to compensate for the wear on the lands in the control valves, mostly the hitch valve is the problem. I usually go for about .040 to start with, as if you go too large your system will not pressure up when you use the valves. But first off, clean orifice, throw away the ball, and try that with original size. You will need a new gasket and also replace the o-ring on regulator piston and polish it up nicely.

Is it the cover facing rearward or the cover facing the center of the tractor?

OK, so I removed the whole unit from the tractor and took it apart. The screen was collapsed and torn so I cut it off the orifice and chucked it in the garbage. There was no roll pin or check ball. What exactly is the purpose of the screen anyways? It seems to me it would be better if a small amount of garbage passed through than to have the screen plug up and wreck your hydraulic system. The orifice size was still .031" and I left it at that. The o-ring on the piston looked good. I polished out the bores good with some 600 paper. I re-assembled the unit and put it back on the tractor. It's still doing the same thing. Now what? Do I need to go larger on the orifice size? What is the small hole that is drilled in the piston at about 45 degrees to the axis of it? I was only able to get a piece of wire a small ways up it.

Start a new thread on the forum. I have reached the limit of the solutions I know on that model. There are several with direct capacity to help. Jim