0ne or two piece driveshaft?

[WB72]

Is there any advantage to either a 1 or 2 piece driveshaft?

I have a Short Wheel Base truck that didn't have a drive shaft. I know there is a place for a carrier bearing, but if I have to build a new Driveshaft, I want to know if I should make a 1 or 2 pieces unit.

I will be running airbags lowered. LS power to come later.

[lutronjim]

My 70 C10 had a 2 piece and the center bearing rubber holder kept going out. If it didn't, the bearing would.

A friend said some of the trucks came with one piece. He found one for me and it was great. I really don't see why they ever used 2 piece in short wheel base.

[WB72]

I'm not sure if there was actually a 2 pc in the truck, there is just the place to mount the carrier bearing.

When I swapped out my trans in my other 72, I ran a 1pc because I had the trans shop decide and they just modified one end of one they had laying around.

Is there any difference in the pinion angle when running 1 vs 2 pc?

[tutone]

I have seen them both ways. I read that a lower geared truck benefits from the two piece. Stronger according to the article.. I shortened my own [two piece] when I cut down my long bed. Not a big deal but just a little time consuming. I wonder if the length of an automatic is one of the deciding factors.

[Keith Seymore]

One piece: fewer pieces to go bad, less complexity, easier to set the u joint working angles

Two piece: enables higher shaft speeds (=higher vehicle speeds) across longer wheelbases; smaller diameter tubing can be used to improve packaging

Originally Posted by Keith Seymore

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).

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, an aluminum/carbon wrap, or exotic materials like "metal matrix" (aluminum impregnated with other metals).

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.

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