It isn't the 3 degrees, it is the
delta between the sending and receiving planes. The U-Joints can easily take a 3 degree prop angle, and these cars have far less than that by design. I will report later when I take the time to draw a sketch, but I am seeing just a degree or two of primary shaft angle on my car. At a 3 degree delta, one would certainly feel driveline vibration, due to the elliptical paths of the U-Joint yokes, and this probably explains a lot, especially in light of sagging engine mounts, etc. This illustrates it very clearly:
https://www.youtube.com/watch?v=gmV4qwLfOMY . As does this one:
https://www.youtube.com/watch?v=LCMZz6YhbOQ .
For example, Tim's engine mounts (and mine to a lesser degree) were shifted by a full inch top to bottom stud (!). This effects Block/Transmission Pitch and Yaw at a minimum. We have been working on removing the vibration from his car for about a year, made a lot of progress in many places (wheels, tires, balance, alignment, rear axle changeout, the usual stuff). Hopefully this study continues the progress.
So far, on my car, I have been able to get the Engine Roll down to 0.20 Degrees (as measured by the Block top face to the Crossmember), and the Delta between the Trans Output and Diff Input at 0.30 degrees. The hot rod crowd (as far as I have researched) shoots for a 1.5 degrees max delta, BUT interestingly, they purposely set the Diff a little low, figuring that the car will squat somewhat during a hard acceleration, the rear axle will lift up, and bring the delta up to almost zero degrees during full power on. Can't do that without spring shims on these cars, of course, as the trailing arms are not adjustable. [The driveline shaft angle itself is never set at zero, i.e. the entire system colinear, which might make intuitive sense, straight through power, because then the U-Joints will see brinell hardening on their yoke bearing rods. The yokes
need to make that elliptical movement].
The Guibo should be as exactly inline as possible to the trans output, and that is easy to achieve, because there are support bars for both the trans support yoke and the pillow block bearing right there, which are easily shimmed! If these are out of colinearity, there will certainly be vibration and wear issues, and it turns the driveline into a (2) shaft versus a (1) shaft system. The rubber Guibo then constantly trying to sort out the delta with every rotation. [With the short section hard fixed to the chassis/unibody and colinear with the transmission output, this is a really simple (1) shaft system, with the only degree of freedom really being the up and down movement of the rear axle. And that isn't much on average, with long training arms.
I find this stuff fascinating, and now on to something else!
