Quote:
Originally Posted by Captainfab
I have seen 2 longbeds with a 1pc driveshaft from the factory. I really don't know what the deciding factor was.
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It has to do with propshaft (aka "driveshaft") critical speed.
Propshaft critical speed not just based on wheelbase but is also based on trans type (length), rear axle ratio, tire size, and engine type (larger engines allowing a higher top speed) AND/OR any strange resonances in that particular combination (camping out on that resonance will break the trans/transfer case tailshaft housing).
One other comment - critical speed is not directly related to balance, but rigidity. When the shaft exceeds it's critical speed it begins to bow in the middle and swing like a jump rope. Hence the disturbance and durability concerns.
You can get around it by going to a larger diameter steel tube - or more expensive alternative materials like aluminum, carbon fiber, an aluminum/carbon wrap, or exotic materials like "metal matrix" (aluminum impregnated with other metals) - or - the cheap way out is to limit the vehicle top speed via ignition or fuel cut off above a certain engine rpm.
So - given two otherwise identical appearing trucks - there could be a tire difference that put it over the edge, or perhaps a different horsepower rating which would allow for a higher top speed, or some unseen bending resonance that shows itself during testing which would drive the truck to get a one piece shaft vs a two piece. A long wheelbase truck with a low (numerical) rear axle ratio spins the shaft slower and might get a one piece, but an otherwise comparable truck with a high rear axle ratio might get a two piece.
K