[Keith Seymore]

Originally Posted by INSIDIOUS '86

The one piece is desirable since it is more durable and less maintenance. Two piece driveshafts were for heavy duty trucks that could reach higher speeds with the bigger engines they had so two peice was don't to keep down critical speed ( the speed in which your shaft turns into a jump rope).

The longer the driveshaft the lower the critical speed, the bigger the tube the higher the critical speed.

Say I put 5:11 gears in a long bed crew truck with a long driveshaft and proceed to drive as fast as possible on the highway. Well you would see some serious sh!t!

The weakness of the two piece is that two peices are not as stable at high speed anyways and the carrier bearings can't hold much.
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Agree -

Here are the words I used in a previous post (to say essentially the same thing):

Originally Posted by Keith Seymore

It has to do with propshaft (aka "driveshaft") critical speed.

What you guys might be missing is that 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).

So - 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.

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 or "metal matrix" (an aluminum/carbon wrap).

So - on the two 350 trucks - there could have been a tire difference that put it over the edge, or perhaps a different horsepower rating which would allow for a higher top speed. I can assure you there was something different there that is not obvious to us after the fact.

By the way, I hate the complexity and mass of a two piece setup and go out of my way to order my trucks such that they get a one piece shaft.

K

K