I agree with everyone's comments so far on this. But there's another thing
worth mentioning. Your chassis will flex a little. If you do a great job in
it you may only be able to measure the flex with a dial indicator. So you'll
want a little ability to flex (universal joints) between the transmission and
rear end unless they're one close coupled unit like a rear engine racer.
Otherwise the transmission and rear end bearings will load up whenever the
looseness in the splines is overcome. In mechanical engineering we call this
an over-constrained mechanism. I'm guessing that if you used a conventional
3"+ dia. tubular driveshaft with splines but no universals you couldn't
practically make a frame stiff enough to get away without universals; and
you'd end up overloading your rear transmission bearing whenever you hit a
bump.
Ed Weldon
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