John Deere 440I Front Hydrulic pump problems

[Rayshobbyfarm]

I have a 1959 440i wheeled tractor with a model 71 loader attachment. The crankshaft driven hydraulic pump is slipping at higher rpm or under heavy load. I am looking for a parts breakdown and service information on this set up.

I am thinking I need to replace the coupling or shaft but would like to know what I am getting into prior to just taking it apart. Any help would be great.