im having a vibration only in 5th gear between 40 to 60 a "droan" i have heard it called driveshaft is balanced pinion angles are correct on trans and rear..is this a harmonics issue with this combo or some other possibility any help appreciated......
I have a similar problem. T-5 on a flathead. Mine happens right around 3K rpm's. Haven't been able to track it down yet.
I have the same thing on my 53 with a T5 conversion. Mine is an incorrect pinion angle. I made a small mistake when i set it and welded the perches to the rear end, and it created a slight shake, harmonics in mine. Mine comes in around 50-55 though.. I have yet to get a chance to take care of it, but after checking everything else, i finally found my goof up..
I would think a trans bearing. What kind of condition is the rear bushing for the slip yoke,also a possibility.
are you using the supports that bolt the bellhousing to the tail? could be putting too much side stress on the shafts. the case is weak to begin with