450 Farmall Power Steering Problem

I need a little help getting to the bottom of a power steering issue on my 450 Farmall. Due to deteriorating power steering, I put a brand new hydraulic pump on my tractor this winter since the old one was flowing about 6 gallon @ 1100 psi or half of new. Pressure came up on rear remotes but still don't get power steering at PS unit(Char Lynn) unless I pull a hydraulic control lever. I've had the pressure regulating valve disassembled a couple times and see nothing wrong. The priority valve is still nice and round and only has about .004 clearance to the bore in the valve housing. The orifice in the priority is .125 or 1/8". I pulled off the control levers and checked the O ring on the plug between the first valve and the casting it's bolted to. It didn't look bad but I replaced it eliminating that as a possible leak. I continue to think I have a problem in my pressure regulating valve but not sure where to go next. Any suggestions?

I would say it is the flow control valve leaking past. They do usually show wear on the lands but, the bore can be worn also and that is a major job to rebuild. You could disconnect the line at the flow control valve and put a gauge directly onto that fitting. It should show you 1200 psi without operating an aux valve. If it does not, then operate the aux valve. If you get 1200 psi doing that, you will know the power steering relief valve is good. The relief valve is a small ball type valve located below the flow control valve. Totally separate from the main relief valve under the top four bolt cover. I have put many new flow control spools in over the years (originally they were not a serviceable part but IH wised up). Last one was about 8 years ago and was still available. I have heard it is no longer available but a good parts man may be able to locate one. If the bore in valve is worn a new spool will not help much. A make shift flow test will tell you also if you are getting good flow at reasonable pressure, BUT, the capacity of the reservoir is so small that it has to be a very short test and probably only catch a quart and calculate gal per min from that.

I'm a machinist so I have the tools and ability to take precise measurements. That being said, the flow control valve spool looks good having no flats worn on it and the bore/spool clearance measures only .003-.004 clearance. When I bought the tractor about 6 years ago I had the control valve spool out due trying to get to the bottom of just the opposite as now. At that time, I had good power steering but no pressure on the rear remotes. This was the first time I ever tried using the remotes. Upon flow control valve spool removal, I noticed the orifice in the flow control valve spool had been drilled way open(5/16") by a previous owner. I presume to improve power steering since it was a loader tractor much of it's life. Due to the huge orifice I don't think the flow control valve spool ever shuttled backing and forth causing wear. I think so much oil could pass through the over sized hole the spool was motionless many years causing no wear to it or the bore. So at that time, I tig welded the oversized orifice shut and drilled it out to first 3/32" then to and 1/8" to achieve some flow balance between decent pressure on my rear remotes and the power steering. This fix worked well and did so 'til last summer when my power steering started to deteriorate. Since then it's been process of elimination to conquer this problem. Any more thoughts? I appreciate the input.