Tractor Repair: 970 case steering, wheel shaft, free wheels

Question
I am repairing a 1984 970 case tractor. the machine struck a tree head on and the steering wheel just free wheels around. I can see the steering wheel shaft go into the gear box. I guess the gear box powers the hydraulic for the steering. My question is does the shaft have a sheer pin at the bottom of the shaft in the gear box. If so is it rebuildable?

Thanks

Answer
  Actually, there is no gearbox on these, and the steering is completely hydraulic.  The steering wheel turns a hydraulic control unit that directs oil to the steering cylinder on the front axle.  There are two types of steering columns, a rigid steering column and an adjustable steering column that tilts and telescopes.  There is a pin that attaches the steering wheel shaft to the hydraulic control unit, but it is not a shear pin and I've never seen one break.  There are lots of parts inside the control unit, but nothing that would shear off.  I don't know what parts are still available for it, and if there are any, they would be too expensive to rebuild it.  I think a better way would be to get a used one from a junk yard, if that's what is actually the problem.  If the shaft turns where it goes into the control unit when you turn the steering wheel, then the column is OK.  You should be able to see the pin that holds the shaft onto the control unit to see if it's OK.  It's possible that the pump is not supplying oil to the steering, but then you should only lose power steering and the steering wheel should not free wheel.  Disconnect the hoses from the steering cylinder on the front axle and see if there is any hydraulic pressure.  If so, then the problem is in the steering cylinder.