Tractor Repair: international hydro 88 will not move., axial piston pump, variable displacement

Question
a friend of mine has an international hydro 88 that will not move. he said it worked fine until it ran out of fuel and his employees pulled it 1/2 mile with a chain back to the farm shop.someone who also owns a hydro 88 told him that serious damage can result from pulling this model tractor but they don't know why.could this be the cause?if so please give a description of how the transmission works and what could be wrong.thanks.

Answer
Hello,

  Yes, pulling it can cause serious damage to the hydrostatic drive motor.  The hydrostatic pump is a variable displacement axial piston pump that pumps oil into a variable displacement axial piston drive motor that drives the differential.  Without the engine running, there is no lube oil supplied to the drive motor so if the wheels are driving the motor, but it is not getting oil pumped to it, the motor will be ruined.  Sorry to have to tell you all this, but if it worked fine until it was towed, then that has to be the problem.

                      Good luck,

                           Arnie