flywheels/manual dont crack...flexplates/auto crack around the crank bolts and around the torque converter to flexplate bolts...ring gear is the outer section of a flywheel/flexplate that meshes with the starter motor pinnion gear to start the motor...ring gears are welded in a few different spots to a flywheel or flexplate and are replaceable...welds will break on flywheels/ring gear causing the ring gear to be out of wack...:Chin: