Flexplate proves to be vitally important in automatic vehicle. A flexplate has a circular steel disc with holes, and teeth on the outside edge of ring which engage the starter. Flexplate is installed to crankshaft flange, and links to torque converter with mounting bolts. Flexplate is balanced to provide smooth engine RPM. Identifying whether flexplate is warped or not entails careful observation and elimination.
Step 1
Start vehicle, and pay attention to noise from starter when it spins and engages flexplate, or torque converter if vehicle doesn’t have toothed flexplate. Please pay attention to if starter has low, medium or high pitched whine when it spins. Notice starter spin that bogs, subsequently picks up again, and bogs again in a rhythmic sequence. These features illustrate flexplate is warped, provided starter works in a proper way and can be ruled out.
Step 2
Listen for rhythmic clunking or grinding noise when engine idles in neutral or park, or idles in gear with foot on brake pedal. Broken or loose bolts on crankshaft end of flexplate, or on torque converter side, miss-align flexplate, leading to the high side of plate to strike or rub against internal parts. Warped flexplate can make metal-to-metal contact with inspection plate cover, or starter drive mechanism, and can make knocking noise as well when vehicle is put into forward or reverse gear.
Step 3
Drive vehicle normally, let transmission shift automatically from the lowest to the highest gear. Driver can shift manually as well, from first gear to second, normal drive subsequently. Feel unusual vibration from chassis. The vibration is heavy, but not as heavy as failing u-joint. Warped flexplate can lead to vibration through all speed range, notably if flexplate is not balanced.