The OE case bushing in vehicles with a GM THM-400, 4L80-E and 4L85-E transmissions tends to walk out of the housing bore. This leaves the output shaft unsupported, ruins the governor gear and can cause case damage. The no-walk flange feature of the Sonnax case bushing 34006-SP is specially designed to keep the bushing 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.