I heard a rumor

[Keith Seymore]

Originally Posted by boatpuller

Mine was built in California. As a diesel. I have run into a few baffling things with that truck that don't follow the book of gas engine trucks.
The short bed two piece vs one piece drive line is another example of having a hard putting a pattern together like the pedals.
Iv'e seen big block 1/2 tons with 1 and 2 piece and small block trucks with 1 or 2 piece in both long and short bed configs.....that one has always intrigued me .

Originally Posted by Titomars

1 or 2 piece drive lines were always determined by total length, trans yoke to diff yoke.
if you get a drive shaft too long it has a nasty tendency to flex in the middle at high speeds.

Almost -

there's a little more to it than that.

K

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).

K