I keep posting in many of these threads that I have run a CF driveshaft for years. It took care of all the vibration issues I had but you still needed to take care of the drive angle issue first.
High rear end ratios (3.73, 4.11) with overdrive trannys is what have made these issues come up.
With the addition of the CV joint I believe you may have taken the angles out of the equation for "reasonable alignment" of the tranny and rear end.
If this works it would be a good new product for some one to sell. Build enough of them and the price will go down.
My CF shaft was about $800 some 5 years ago now. Another 200 for the CV joint and I wouldn't complain.
You have made some excellent points. A carbon fiber driveshaft alone should result in much smoother operation provided that the angles are right. By "right," I don't just mean aligned front and back, but also not too large. Mark Williams has an excellent service bulletin here:
You can see that there are two factors to consider: critical speed and working angles. While most of us don't consistantly race our cars so the critical speed may not be a huge issue, the working angles are a concern.
Take for instance a combination that is not so uncommon; 4.10 gears, overdrive transmission, and a 285/40-17 tire, which is 26" tall. A 4000 RPM driveshaft speed is reached between 75 and 77MPH!!! Now look at the chart on the Mark Williams service bulletin. At 4000 RPM driveshaft speed the maximum recommended working angle is only 2.75 degrees.
I don't consider my setup to be that unique. I am using standard engine frame stands and engine mounts. My transmission is only slightly longer than a Muncie and is certainly more compact than a TKO or a T56. My transmission tunnel is mostly stock with the exception of extra room for the shifter linkage. My car is lowered some, but really not as much as some others. The more the car is lowered in the rear, the more severe the issue becomes. In order to get the working angles below 2.75 degrees, the rear of the transmission has to be raised. The lowest working angle I was able to achieve was 2.5 degree before the slip yoke started to make contact with the top of the driveshaft tunnel. So for cars that are not lowered, the working angle issue is not a concern. But for many that want a lower stance, angles become a critical factor to consider.
I said before that what I am doing is probably overkill. As Ron has stated, I probably could have just had a CF shaft made and it would have been fine. But given the time and energy that I have expended dealing with this issue, I wasn't about to take any chances. I wanted a solution that would address both the angle issue and have the added benefit of damping the driveline.
Adding a CV to the front require some custom machine work. There isn't a yoke that is currently manufactured that will allow the CV to be bolted to it and work with a 32 spline GM output shaft. So part of making this shaft includes the modification of a Spicer yoke so it will accommodate the CV. The cost of doing the modification and the CV itself adds an extra $450 to the cost of the CF shaft. DSS sells regular CF shafts for around $1000. I feel that they have done their research on the challenges involved in making a CF shaft, thus I am comfortable with their process. Here are some more details about what makes their CF driveshafts different from others:
My configuration represents the extreme in cost. If working angles are a problem, a CV shaft with an aluminum tube may be just as effective. If the angles are right, but there is still a vibration, a conventional shaft with a CF tube may do the trick.