Thust bearing wear causes crank walk or "crankshaft end play". More common in manual transmission applications but can happen in automatics as well. Thrust bearing failure can be cause by excessive pressure or force from the transmission side of the crankshaft. Sometimes "lugging" a manual trans car can cause premature wear of the thrust bearing. lugging meaning pushing 4th gear at 1,500 rpm's when you should of grabbed 2nd or 3rd. Also I guy with a large hammer installing a harmonic balancer can cause thrust bearing failure.
And in our case, tone wheel damage as well. I think some of the early tone wheel explosions that took out pistons, were after pulley sets were installed.
