I just finished a rotisserie restoration on a 1971 GTX 440 auto 8 ¾ with a 323 posi. I am experiencing a on and off type vibration with begins at 40mph - 65mph. It may continue past 65 but that is as fast as I have driven the car since completed.

I have placed the trans in N while rolling down the road and the vibration continues even though the engine drops down to an idle.

I am running tapered bearings in the rear axels set at .010 .012. The bushing was replaced in the tail shaft of the trans during its overhaul. The drive shaft is brand new and I also tried to but the old shaft in and it did not make a difference.

The center section is a 489 case and was rebuilt using the original ring and pinion.

Everything is brand new or rebuilt on this car. It was restored to factory specs with no performance modifications. I am stumped.

Any input would be appreciated.

Thanks