I'll try this again....

[Keith Seymore]

One piece vs two piece is determined by the shaft critical speed (the rpm at which the shaft starts to bend).

Inputs to critical speed calculations include: wheelbase, shaft overall length (a function of wheelbase and also transmission length), shaft material, tube diameter and wall thickness, rear axle ratio, tire diameter (and speed rating) and anticipated vehicle top speed, as well as any unforeseen destructive system resonances discovered during physical testing.

Changing any of those can make the difference between a particular model getting a one piece or a two piece shaft.

I could envision a small displacement 2wd lwb truck getting a one piece shaft, especially with a lower numerical rear axle ratio, due to a potentially lower top speed and the slower shaft rpm due to the axle ratio. Higher horsepower engines, allowing a higher vehicle top speed, might drive the design into a two piece shaft (or a one piece shaft of more exotic materials). Speed limiting the vehicle, through fuel cutoff or ignition rpm limiting, or releasing a lower speed rated tire, could put you back down in the range when a one piece shaft would be acceptable.

K

http://67-72chevytrucks.com/vboard/s...light=critical
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