For years this argument just amazes me. The parallel driveline guys set up there leaf spring suspension in their beautiful hemi whatever and argue nonstop about that is the way it needs to be because the ends rotate at different speeds yet never once thinking about how there drivetrain is NOT parallel on the 20 mile trip to the car show. Their drivetrain may never ever see that parellel unless they are at the track and have made a nice clean pass.
But for us driveshaft angle guys, we can argue that the parallel guys are wrong if they set up there drivelines with a positive angle at the rear joint. And this is the reason why we say not to use the parallel method.
For the first part. The drive shaft in cruise mode is lightly loaded and doesn't need the maximum strength that a dragstrip pass requires. And being lightly loaded the extra movement shouldn't cause excessive wear. Also, I am a firm believer that if a leaf spring car rotates the axle more than 3-4* under power, that steps need to be taken to limit that rotation. I believe the x-tra angle in the cruise mode to correct the angle under power is the lesser evil to bandage a poor suspension design. Leaf springs, by nature, are incorrect for the application - a spring is intended to store and release energy, not transmit power. Look at the "bandaids" for them - all fixes either stiffen the front segment or lock it out completely.
As to the second part. If under power you have -3* at the front and +3* in the rear. The driveshaft is parallel. The pinion is driven at a constant speed. How is the rear joint any weaker? 3* operating angle is 3* operating angle, period. The u-joint doesn't know or care - or +. Angle is angle. It has "X" strength at "X" angle - PERIOD. So please show me how the joint can be weaker simply by flipping it over?
