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 bushing 34006-SP 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. When damage to the case is so severe that bore diameter is larger
than 2.129", use Sonnax oversized case bushing 34006-OS. See instructions for details.