Lack of flange or stop surface on the case bushing.
These no walk-out case bushings are flanged to prevent movement in either direction.
The OE case bushing in vehicles with a THM-400 or 4L80-E transmission tends to walk out of the housing bore. This allows the bushing to wander into the extension housing, leaves the output shaft unsupported, and may ruin the governor gear and cause case damage. Sonnax oversized case bushing 34006-OS for severly damaged cases is specially designed to remain in the case bore.
The housing bore should measure between 2.1285"/2.1295" in diameter for an ideal fit. If the
bore meets this measurement, use Sonnax standard-size bushing 34006-SP. See instructions for details.
Contact a Sonnax Parts Distributor.