I don't think it's the transmissions, neither is it the bellhousing or clutch, those are all proven parts. It's probably a combination of install error, or people simply not knowing what they're doing even with instructions on hand (some people still install these without aligning the bellhousing, a big NONO with these mdoern trannies, they have nowhere near the free play on the input shafts that for instance an old muncie has, they are much less tolerance to off axis positioning)
Then there's the issue that SolidLT1 brought up, and if his has it there must be others out there. The mismachined yoke will cause a vibration because the joint is not clamped down.
Then there's the obvious transmission & diff alignment. A lot of people don't do it with an inclinometer, do it by trial and error or not at all. Factor in the number of twisted frames and it's a recipe for problems.
I've had really bad vibrations after I installed the TKO. I bought a $8 angle finder at HomeDepot and checked the angles. The transmission tail was pointing down 3 or 4 degrees and the differential was also pointing down 2-3 degrees.... I cut the differential poly cushion to raise it and I shimmed the transmission mount to raise the transmission also.... now the trans is pointing down 1 degree and the diffy is pointing up 1 1/2 degrees, at least that's what the cheap angle finder tells me.... vibrations are gone bye bye... smooth as silk now :thumbs:
As TT pointed out, alot of the vibration issues are because of installation errors or a driveline angle issue.
I have yet to hear of a defective transmission or internal part in the transmission that was the cause of a vibration. I am not saying it isn't possible, only that I have not seen one yet.
SolidLT1 has posted that he has a yoke of ours that the u-joint cap is not seating in the journal properly even with the caps tightened down. While I have not seen this yet, I am very interested in getting to the bottom of this. In my mind, if the cap is loose in the journal, then yes, it would cause a vibration and needs to be corrected. I have offered to swap it for him at no charge even though he wasn't our customer(directly). Hopefully I will hear from him soon.
I take my job very seriously and do not want an unhappy customer out there, nor do I want a defective part out there in somebody's car.