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The power steering circut is a priority circut. Nothing you do should cause any change in steering function. Oil is drawn from the bottom of the rear housing, through the hydraulic filter, through tubes cast in the clutch housing, to the steering (MCV) pump. From the pump the oil goes first to a flow divider/priority valve. The flow divider is actually two pieces. Oil goes to an an orfice that allows 5 GPM (3 GPM on 66 and older series) priority flow. Excess fluid is diverted by the flow divider valve to lube the differential. This flow varies with pump speed and condition but the 5 GPM remains constant. A worn pump or a serious leak will cause this flow to diminish to the point where no flow will go to the differential. This is the major cause for rear end problems in IH tractors. The 5 GPM flow from the flow divider goes first to the steering system and then steering relief valve. This limits the steering pressure to 1600 to 2100 PSI, depending on the tractor. Return flow from the steering and/or steering relief valve is still 5 GPM. One GPM of this flow is used to lube each brake, leaving 3 GPM for the TA control valve, brakes, seat, and hydraulic clutch assist. Pressure in this circut is limited to about 240 PSI. The TA, clutch, brakes and seat are all closed center valves that use oil only while being operated. Oil left from this circut is directed to the TA lube circut. It is limited to about 20 PSI. Any oil above the 20 PSI is returned back to the sump. Loss of steering while the clutch is depressed can be caused by a weak pump or leak AND a stuck flow divider valve. Any loss of steering assist can be an indicator that the differential is not being lubed properly. It is critical for the steering to function properly to get long life out of the differential and ring gear and pinion.
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