I am running a Kpower ZF5 kit in my car with their old style driveshaft. The driveshaft is connecting to a getreg differential.
There is a terrible vibration that I am most certain is coming from the driveshaft. My angles are parallel with each other, and I have enough operating angle in the universal joint, (to allow them to operate and not "seize up")
I measured the pucks that adapt the driveshaft to the diff, and driveshaft to trans. There was a decent amount of play which I think contributes to the vibration. I was able to set up a dial gauge and indicate the pucks to the diff and trans, but there is no where to measure and indicate the driveshaft to the pucks themselves.
I checked the rotation that the universal joints were welded onto the shaft, and they are off by 2.8 degrees, so those are not in phase which is a problem.
One of my universal joints also has a tight spot which is weird after only a year of running it.

I am pretty shocked with the lack of good things about this driveshaft, and I am glad that Kpower changed their supplier and design for them.

I reached out to them and they are willing to help me out a little but I wanted to know specifically what options are out there for my setup.
Do you guys know of any reworks with this shaft? Does a re balance help? Should I find a shop to cut and reweld the universal joints in phase?
Kpower has been good with emailing me back when I have questions but I don't necessarily want to buy their "updated" shaft when they sold this one with problems.

 

It's an on going issue as far as I've read, with limited fixes. I'd try the driveshaft from the new supplier, rechecking all of what you've already checked on the new shaft.

I do a ton of aftermarket driveshafts in my line of work, including a ton of BMWs. They all try to swap from the standard 2 piece to a one piece aluminum or steel unit, due to various diff or transmission swaps. I'd say roughly 75% of them have vibration issues. We've solved a few by going back to custom 2-piece driveshafts, but I don't think that's feasible or necessarily the problem with Miatas. My point is, it's not just K-power, or just you. Driveshaft shops that'll do a "perfect" one off custom driveshaft are difficult to find, if you have a bolt in new supplier with a small discount, I'd say it's worth the risk.

 

You could try looking in the thread where all the ZF guys talk about how their driveshafts vibrate and discuss what they've done to try and fix it.