Driveline Question

[stepsider]

My 71 GMC Stepside short wheelbase has a 2 piece Driveline. Should I go 1 piece driveline,

[davepl]

Is there a problem you're trying to solve? GM didn't use extra parts when they didn't need to, so there's some benefit of a two-piece, or at least they thought so at the time...

[DonnieB]

I have a one piece I would trade ya if you want a one piece. I cant run it due to it hitting when I air my truck out. PM me if you are interested.

[mechanicalman]

Originally Posted by stepsider

My 71 GMC Stepside short wheelbase has a 2 piece Driveline. Should I go 1 piece driveline,

Depends on what you want, it's your truck but if you do make sure the driveshaft geometry is correct, and that may involve some shimming of the trailing arms to the axle pads, or relocation of the front trailing arm mounts. They also make "drop members" if you have a certain amount of drop, not sure how much but if you have lowered it a lot and the angle is not correct that's one way to go.
https://www.google.com/search?q=chev...0drop%20member

A certain amount of change can also be had by removing the rivets holding the front trailing arm brackets to the cross-member and either moving it up or down by drilling extra holes or turning it upside down, just depends on how you need to go and how you want to do it. Shimming the pinion angle of the rear axle pads is probably the easiest way to go for minor adjustments.

As you see in the pictures, wrongs and rights. The R side picture with the red frame/tires, A is incorrect and B is correct.

[Keith Seymore]

Originally Posted by stepsider

My 71 GMC Stepside short wheelbase has a 2 piece Driveline. Should I go 1 piece driveline,

Yes, if you can.

Previous discussion:

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

[stepsider]

Alot of good input, I plan to drop the rear 4", 2" with springs & 2 with blocks. Which is a good combination springs & blocks ? Also going 4" is 1 piece or 2 piece Better with this drop ?

[mechanicalman]

Originally Posted by Keith Seymore

Yes, if you can.

Previous discussion:

Don't think we missed anything based on your post.

It's a short wheelbase as specified by the OP. On light trucks, the only 2pc drive-shafts on this era truck that I have seen have been on trailing arm suspensions, and I always assumed (gulp), that it was because of the pivot point of said trailing arm mounting point and the associated geometry.

That being said, I would like to ask you a question: How does the stability of the pinion angle of the trailing arm C10 suspension relate to the 2pc vs 1pc driveshaft in regards to stable angles throughout suspension travel? Is a 1pc a bad choice if the trans tail-shaft is forward of the trailing arm pivot point? I believe it travels in an arc vs the somewhat erratic movement of the pinion of the light truck leaf spring rear axle (axle wrap, shorter pivot point).

Interesting NASCAR has used this type system, I think they used 1pc drive-shafts but not sure where they located the trans tail-shaft in regards to trailing arm pivot point.

[Keith Seymore]

Originally Posted by mechanicalman

Don't think we missed anything based on your post.

It's a short wheelbase as specified by the OP. On light trucks, the only 2pc drive-shafts on this era truck that I have seen have been on trailing arm suspensions, and I always assumed (gulp), that it was because of the pivot point of said trailing arm mounting point and the associated geometry.

That being said, I would like to ask you a question: How does the stability of the pinion angle of the trailing arm C10 suspension relate to the 2pc vs 1pc driveshaft in regards to stable angles throughout suspension travel? Is a 1pc a bad choice if the trans tail-shaft is forward of the trailing arm pivot point? I believe it travels in an arc vs the somewhat erratic movement of the pinion of the light truck leaf spring rear axle (axle wrap, shorter pivot point).

Interesting NASCAR has used this type system, I think they used 1pc drive-shafts but not sure where they located the trans tail-shaft in regards to trailing arm pivot point.

I would suggest that the longer (ie, one piece shaft) would be better because the added length helps minimize the angle change through suspension travel.

The fact that the two components (drive shaft and rear suspension) are traveling on different arcs is immaterial because the change is taken up in slip at the slip yoke. For example, the difference in attaching points is even more dramatic on a leaf spring equipped vehicle vs a trailing arm suspension (and doesn't cause a problem).

If I understand your comment/question correctly -

K