UPDATE: I think I jumped the gun and now I have to swallow my pride for thinking I had fixed the issue
. Phasing the rear shaft as mentioned earlier eliminated the vibration in the clutch pedal 100% and reduced the vibration in the drivetrain considerably....but not all of it. There's still an issue. The vibration now starts at 60 mph and gets worse with speed. I removed the front shaft and drove it to work yesterday (60 miles) and it didn't change anything so I can rule the front shaft out. Last night I reinstalled the front shaft and once again removed the rear. Tonight I will take it for a drive and see if the issue is gone. I will be happy if it is as I'll know it's the rear shaft that's the issue.
After a bunch more research on Double Carden (CV) operating angles, I think I finally have a clear understanding on how to set them up. I'm about 90% sure that my pinion angle is wrong and that's my issue. I had read that the pinion should point directly at the tail-shaft so I determined I needed 3* shims to raise the pinion up. That wasn't exactly correct.
To understand this you have to completely ignore any thoughts on how to set the angle on a common Single U-Joint type shaft. Forget it! Since the CV has 2 opposing u-joints in the "head" they effectively cancel each other out. Whatever angle is created between the output shaft and driveline is split 50/50 between these two u-joints. It DOESN'T matter what the angle is as long as it doesn't exceed the capacity of the u-joints. Now, the driveshaft points directly at the pinion shaft. Since there is only one u-joint on the rear of the shaft, it has nothing to cancel out its operating angle so it MUST be exactly in line with the pinion to avoid vibration. No exception.
However, this is not the end of the story and where most people (me) go wrong. This is a static setting. When the vehicle is in motion, torque is being applied to the ring and pinion to overcome friction to keep the vehicle moving. This causes spring wrap which causes the pinion to rise, thus changing the static angle by several degrees (2-4 seems to be the consensus). To avoid vibration AT OPERATING SPEED this additional angle must be factored in the static setting.
In my case, I added 3* shims and got my pinion .5 degrees higher than my driveshaft slope at static. Close enough, I thought. So, I'm starting off .5 in the wrong direction and adding several degrees more in the wrong direction at speed. At 60 mph, I'm guessing my pinion angle is 3-5 degrees off. This makes sense because the angle (vibration) is not noticeable around town at slow speeds. Since I have a newly rebuilt trans and t-case with all new bearings and new balanced driveshafts, it doesn't seem logical worn parts could be an issue.
The tricky part of getting the pinion angle correct is that you have to install the driveline, measure the shaft slope and adjust the pinion angle 2-3 degrees lower. However, big note here, when you lower the pinion, you lower the end of the driveshaft, thus changing the slope. It's a feedback loop that can drive one crazy. I think the easiest way to do it is to loosen the axle U-Bolts and use a jack under the front of the diff and jack it up to rotate the diff while measuring the driveshaft slope and pinion angle until you hit that magic -2 degrees. Then determine what angle shims you need.
This weekend I'm going to remove the 3* shims and go back to the way it was. That may be all I need (+.5-3=-2.5), essentially what I started with. lol. Stay tuned.
