I have a '72 GS 455 and want to upgrade to a 4 speed overdrive. The car had a th350 put in it by the previous owner and it appears that the output shaft bushing or shaft is faulty. I was experiencing driveline vibration and significant trans fluid leakage even with a new seal I installed. Then I installed a new driveshaft which was balanced and a rear seal and it still vibrates and leaks. I took the trans tailshaft housing off and the bushing is beat up with numerous abnormal grooves making me believe that the shaft is oscillating too much. Since I have to remove the trans anyway I am contemplating an upgrade. I have been told that the th200r4 has the correct bolt pattern but has to be substantially upgraded to handle a big block And that the th700r4 does not have the correct bolt pattern. Any input or advice would be appreciated.
