Cause it neck down to something like .400 of inch about 2.5 inches into the pump. Shaft is nice and thick for the pulley. I am thinking its a designed break point, as not to over pressure the sytem, likely the last fail-safe if to pressure releif valve can't keep up. As not to screw up other $$$$ive crap.

 

same thing happenend to me, when i waS cutting a donut,,,, BAM then lost steering., I fixed it myself, 30 bucks at auto store.