So how important is the plastic coating on the spline shaft?
On the male spline, the coating is gone on the major diameter (peaks) but is still in the minor diameter (valleys).
Will a D2/DC shaft work on an unlifted D1? The price at Lucky8 is not bad on the D2 shaft compared to the D1 shaft they have listed.

 

After replacing the universals in the front shaft and with about 1,000 miles on them I have developed strong vibration around 25-30 mph. Can feel it in steering wheel. I can move the spline joint up and down, easily.
Can I use a D2 front shaft? Lucky8 has a decent price on them.

 

Did the two halves of the driveshaft separate at any point? I ask because the ujoints in the stock D1 shaft are out of phase, meaning the yokes don't line up perfectly like other shafts.
If the shaft was apart at one point and not aligned properly on reassembly that could be your vibration.

 

What is the major source of imbalance in a drive shaft? The placement of the U-joints or the 'phase' of the shaft itself?

In other words can a slightly off kilter U-joint cause vibration? Or is it the proper coincidence of the male and female ends of the shaft?

 

" In other words can a slightly off kilter U-joint cause vibration? Or is it the proper coincidence of the male and female ends of the shaft? "

Yes, and yes. From Rave to show ujoint/yoke alignment>>>

 

Yes, I separated the two halves of the shaft. I marked/scribed before disassembly. That is when I noticed that the plastic coating, Rislan, was worn away.
The vibration in the steering wheel is now gone since I greased the crap out of the rear universals. They need replacing and I'm just waiting for the weekend.
It is not the death wobble. Had it when I first got it but it went away after doing several lock to lock figure 8's in my yard.

I just don't like the flex at the spline.