One piece drive shaft vs two?

[Number21]

My '73 K20 has a single piece drive shaft in the rear, it's the first time I've seen one of these trucks like that. It's huge too, like 4-5" in diameter. All the others I've seen have the two piece with the extra bearing in the middle.

I'm just curious, why does my truck have the one piece shaft, and what difference does that make? Is that just something they did on all the earlier trucks?

[wilkin250r]

I thought the split driveshaft was only on two-wheel drive long beds. Correct me if I'm wrong...

[cory d]

i have a 2 piece on my 2wd short

[Keith Seymore]

From an earlier post -

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).

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.

And - relative to the 454 - that's the setup. In fact, those are the parts we ordered and duplicated when we converted our little white '85 stepper into the race truck.

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

[Dooley]

As examples, my 1977 and 1979 K30 duallies had a smaller diameter 2 piece/carrier bearing setup. Both trucks powered by 400sb and T400. The 77 had 4.10 and the 79 had 3.73 rears. Both were running L78-16 tube type tires.
The 77 K30 was having early carrier bearing failures. The dealer replaced a couple under warranty. They even had the truck on a chassis dyno checking it for vibration/problems before replacing one of them.
For some reason the 79 K30 would trash a carrier bearing in less than 10K even though universal joints were A-1 condition and everything synchronized as it should be. I had a new one piece shaft built and never had any problems again. The front section of the 2 piece setup had a tube length of just 14". The new one piece driveshaft had a total length of 59.5".
The 1988 V30 has the large diameter one piece slip yoke driveshaft behind a 454, T400, 3.73 rears, and 235/85-16 radials. No problems with that setup to date.

[MilkyJoe]

I would swap to a one piece, my s10 had a dual drive shaft (longbed) and the thing ALWAYS had something going wrong with it.

noises, rattles and vibrations.

Maybe the big trucks are of better quality, but I will never have a truck with two shafts again