Knocking/Grinding Noise With Engine Running (Replace Flywheel)

Some customers may comment about knocking or grinding noises with the engine running. This condition could ultimately result in a loss of drive and reverse ranges, or grinding noises during starting.

The condition may be caused by lack of proper alignment between the engine and the transmission centerlines resulting from improper engagement of the transmission housing on the dowel pins. This misalignment causes the flywheel to stress and crack. The condition may be aggravated by the dowel pins being pressed too far into the cylinder block.

1. Remove or disconnect the transmission from the vehicle per Section 7 of the Service Manual.
2. Replace flywheel and retainer if damaged.

Notice: If the torque converter bell housing dowel pin alignment holes are damaged and the bell housing is not replaced, then repeat flywheel damage is possible.

3. If the dowel pin receiving holes in the bell housing are damaged (elongated) due to improper dowel pin engagement, then replace torque converter bell housing. Damage to the torque converter bell housing dowel pin alignment holes occurs during improper installation of the transmission. If the transmission is not installed evenly prior to the bell housing bolts being tightened, then an alignment pin may shear aluminum from the torque converter bell housing alignment hole causing it to be elongated. This elongation results in the misalignment of the engine to transmission. Also, replace the torque converter bell housing if damaged by flywheel material.



4. Dowel height should be 5 mm -- 7 mm (0.197 in-0.276 in) from the engine rear block face. If the dowel pin height is LESS THAN 5 mm, then remove or pull the dowel pins out to the correct height using Kent Moore tool J 23907 (Slide hammer) and adapter J 41988. The dowel pins should then be reinstalled carefully in the engine rear block face using a soft-faced hammer (to avoid peening the dowel) to a protrusion of 5 mm-7 mm (0.197 in-0.276 in).

Important: If the flywheel is cracked near the mounting holes at the crankshaft flange, but the torque converter is still able to be turned by the flywheel, then do NOT replace the torque converter.

5. Inspect the flywheel carefully. If the flywheel has completely separated near the mounting holes at the crankshaft flange allowing the crankshaft to turn independently of the flywheel, then replace the torque converter. When the flywheel is completely separated as described, there will be a lack of needed support for the torque converter. This lack of support causes the torque converter pilot nose to ride on the crankshaft pilot hole causing damage to the pilot nose. When replacing the torque converter for this condition, inspect the torque converter bushing for damage and wear.
6. Review starter operation and determine if any damage occurred to the starter. If starter is damaged, replace the starter.
7. Install transmission while insuring that the transmission is seated on the engine rear block face and is properly located on the dowels. Tighten the bolts that extend through the doweled holes first. Tighten the remaining bolts.
8. After the vehicle has been repaired, test drive the vehicle to determine if any additional concerns exist.

Parts are currently available from GMSPO.

For vehicles repaired under warranty, use: