The last converter that I had that broke plates, broke 2 of them. It turned out that the snout was just a little too big to let it seat all the way into the back of the crank. That caused the flex that cracked the plates. Ground the OD of the converter snout down a bit so that it would fully seat into the crank and no more broken plates. I have found another new converter whose snout was just a little too large, too. Shaved it down a little and have had no problems with it's plate.