Truck Repair: flex plates keep breaking, chevy garage, chevy silverado

Question
I am asking this question for my son. He has a 1997 Chevy Silverado 3/4 ton 4x4 entended cab automatic   5.7 liter small block  350 vortec   has new transmission, new torque converter, new universals and carrier bearings but it keeps breaking flex plates (the 4th one) has a vibration when you first take off, or have a load or pulling something, does not do it in park, only when you first take off. Its been replaced recently but only lasted 9 days. Even Chevy garage can not figure it out. Please help. Thank you.

Answer
Hello Vicki,
Remove the belt from the front of the engine, and carefully pry the crankshaft to the front, then to the rear, to see how much travel there is. You may have a worn out thrust main bearing, or a soft journal on the crankshaft that is allowing too much travel of the crankshaft.
Also possible the rear main bearing is worn, allowing the crank to move off center too much.

One other possibility is the starter could need shims. If it is too close, the bendix could be causing too much pressure on the flex plate, but that would be unlikely, but still, possible.

Van