Have a 1970's, MF135, Perkins, with factory power steering. Steering went out several years back and finally got around to fixing it. Took Pwr Str pump and Steering Gear Assembly to MF Dealer for rebuild. Pump was rebuilt and tested. Steering gear assembly: had Steering cylinder with all of it's associated parts replaced and Steering Control valve replaced. Tractor is at MF dealer and they are unable to get power steering to work. After many hours of research and calls over the US, still unable to get P-S to function. Pump pressure is 1200 psi and flow is within spec's. Inspected steering control valve to measure distance spool would have to move to allow full porting of oil to steering cylinder (+/- 0.25"). And the spool would have to move at least +/- 0.08" to start porting oil into the steering cylinder. I took some crude measurements of the steering shaft up/down movement: up 0.070" and down 0.045". So, steering shaft is not moving up/down adequate distance to move spool in steering control valve to port oil into steering cylinder. What determines the up/down movement of the steering shaft??? Anyone have a hydraulic schematic for Power Steering??? Tractor has been down for 4 months and got to get it going. Sure would appreciate someone sharing their knowledge and experience......