Evenin!! Sounds strange but my 78F150 S/Cab 4x4 with 32:11.50 x 15s' on chrome spokes with 32lbs in all four has started being almost impossible to turn to the right at low speed or when parking. Turns to the left just fine with 2 fingers but have to rev up and put my shoulder in it to go right. Full of fluid, re-tightend belt, box look to be fairl new. Could just be worn out ps pump , but wanted all of your imput fist. This is the friendliest site i've ever been to and I thank any of you who respond in advance.

JMYLEW 78F150 S/C 4X4

 

Might try flushing the system, if it was the pump it would be doing this in both directions. Sounds like the valves are stuck or gummed up in the box itself. Check for any binding in the steering shaft, steering linkage, u-joints, hoses, ect., when turning right. For the fluid, don't mix different types(type F and dextron III)they don't take well to this. Good luck and hope this gets it turning for you. Chuck P.

 

I've had this same problem, I rebuilt the gear box 3 times before I mixed parts from another gearbox. I found that there is a complex valve attatched that is part of the input shaft. It flexs very little when you turn left and right and releases hyd. pressure to assist in turning.
just my 2 cents