Why a 2 piece driveshaft?
 

Does anyone know why the 1967 - 1972 Chevrolet C10 had a 2 piece drive shaft? I am replacing mine with mixed results. Advanced Auto Parts shows one picture and has a different part in the box. Auto Zone doesn't have it and NAPA was more expensive. I'm waiting to see what O'Reilly has for me now. That made me wonder why it's 2 pieces. I've had other cars and trucks that had drive shafts that long and there was no center support bearing.

Re: Why a 2 piece driveshaft?
 

It's a general rule that if the driveshaft is more that 72" then it needs to be two piece or it won't balance right.

Re: Why a 2 piece driveshaft?
 

As a drive line gets longer the critical speed goes down you can increase the critical speed by using a larger, thicker tube or both. Critical speed is the point where the drive-shafts rpm's match the frequency of the material and begins to bend off its centerline.

Good reading here>>> http://www2.dana.com/pdf/J3311-1-DSSP.pdf

Ujoint listings here w/dimensions>>>http://www2.dana.com/pdf/K350-1-DSSP.pdf

Re: Why a 2 piece driveshaft?
 

So there..

J.

Re: Why a 2 piece driveshaft?
 

if u need a new drive shaft find a reptual shop and have it built

Re: Why a 2 piece driveshaft?
 

Could it be that the leaf-spring chassis had a one-piece and the coil-spring chassis had a two-piece? I'm just asking and have no clue. My '96 GMC has leafs and a one-piece. My '69 has coils and a 2-piece. As long as the u-joints are good and properly installed and the center bearing is also good and the rubber in it is good, what is the problem?

Re: Why a 2 piece driveshaft?
 

short or longbed 2-piece..they had those too..

If you need a shortbed driveshaft one piece to replace the 2 piece, you simply get a driveshaft out of a mid 80's 4door caprece...Its a bolt in..and easy to find..

Re: Why a 2 piece driveshaft?
 

My 68 GMC is leaf and it has a 2 pc shaft.

Re: Why a 2 piece driveshaft?
 

Are you serious? I am turning mine into a short bed and I need a drive shaft. Does that mean it will bolt on for an automatic or manual transmission?
And what is the length of it? do you know it off hand?

Re: Why a 2 piece driveshaft?
 

I'm thinking it's the transmission.... My neighbor has an original 72 stepside w/coil springs and it has a one piece.

Re: Why a 2 piece driveshaft?
 

That sounds real promising. You have any pictures or other info? :metal:
s/t

Re: Why a 2 piece driveshaft?
 

When I made my comment, I meant for it to say that I didn't know and was just making a comment. I have no proof. My SWB has a small block and a TH400, as well as a 2-piece driveshaft.

I can see why longer wheelbase vehicles have multiple section driveshafts, so the mystery has been the subject of this post.

Re: Why a 2 piece driveshaft?
 

I don't know either, and I'm just adding what I know to help narrow it down.
Both my neighbor and I have short beds. Mine is 350 auto with coils = 2 piece.
The short step manual trans w/ 1 piece.

Re: Why a 2 piece driveshaft?
 

I'm not sure what the logic is why some have 1 pc and some have 2 pc, I was just saying what I have. I knew you were just throwing ideas out there, I wasn't bagging on you or anything.

Re: Why a 2 piece driveshaft?
 

It will fit the auto ,Yes right length for v8 auto.. some are 54 inches weld to weld,depending on what trans they has..200R4 or 700r4..

the later 86-up are 55 inches weld to weld When you get your truck back together,take your old one,slide it in the trans where the yoke normally rides,then just measure it..and go to the yard and pick one out.

That way you know..I worked at a big yard years ago..and you found what worked..

Re: Why a 2 piece driveshaft?
 

Mine is a short bed flare side with a 2 piece shaft. I had a 1976 Ford with a 8 foot bed and it had a one piece shaft. The length thing makes no sense. All of the older cars that were huge had one piece shafts with or without coil springs. Think of the old Buicks, Olds and Packards. My shaft is fine. I'm changed transmissions and now I'm replacing the u joints and center bearing. My last truck was a '68 long bed and sent from a 3 speed manual to a TH350 and we kept the same driveshaft.

Re: Why a 2 piece driveshaft?
 

They all came from the factory with a two piece driveshaft, long bed or short bed. If they have a one piece driveshaft, it's been converted.

Re: Why a 2 piece driveshaft?
 

to answer your question, I like my 2-piece because it doesn't have the same vibrations that every single 1-piece in my lowered trucks has.

Re: Why a 2 piece driveshaft?
 

The "critical speed" post is correct.

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).

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.

K

Re: Why a 2 piece driveshaft?
 

I guess I'll accept that. It just seems odd that some longer vehicles have one piece and a shorter C10 has a two piece. Perhaps it's due to the diameter of the drive shaft itself.

Re: Why a 2 piece driveshaft?
 

I've had two shortbeds, one 1972 250 6 cylinder with a turbo 350 all original, and a 1971 250 6 cylinder with a 3 speed manual, and both have had one piece driveshafts. There is not even anyplace for a carrier bearing to mount to on either one. There are holes in the crossmember that the trailing arms bolt to, but it doesn't look like there has ever been anything bolted or rivited to it.

Re: Why a 2 piece driveshaft?
 

Have a drive shaft shop make a one piece. They will tell you how to measure it. Take the bracket that the carrier bearing bolts out of the truck.

Re: Why a 2 piece driveshaft?
 

Yep - the '73/'74 SWB 454 trucks had a two piece shaft. There's so many more variables than just wheelbase.

In the GMT400 and GMT800 versions we started using "exotic" materials like aluminum and carbon fibre wraps in larger diameter shafts - all with the motivation of taking some of those two piece applications and turning them into one piece (saving the additional center bearing hardware and complexity).

Believe me, the engineers wanted one piece shafts wherever they could get away with it, too.

K

Re: Why a 2 piece driveshaft?
 

cars didn't tow or get loaded down with 1000lb or more..

Re: Why a 2 piece driveshaft?
 

Actually, quite a few GM cars began using 2 piece shafts as far back as the late 50s. This wasn't done because of shaft length or loading, but rather to allow a lower floor hump or accommodate an X-frame. Other makes may have done this too, but I happen to be personally more familiar with GM.

Ray

Re: Why a 2 piece driveshaft?
 

Here's a better explanation >>>> http://www.engineersedge.com/bearing...ing-bodies.htm

Re: Why a 2 piece driveshaft?
 

That's what I said - "...it'll swing like a jump rope".

:lol:

Makes me think of a joke: this engineer takes his tire into the Goodyear store to get it balanced. While he's watching the work get done (...because we always have to watch to make sure it's done right -lol) the young tire tech takes the weight displayed and splits it in two, putting half on the outboard face of the rim and the other half on the inboard face of the rim.

He asks the engineer: "do you know why I did that?"

The engineer clears his throat and says, "why, yes, in fact I do. If you were to put all the weight on one side, the offset of the wheel introduces a moment, the resulting force being proportional to the lateral distance of the offset and increasing with vehicle speed. The resulting magnitude can create a disturbance which can magnify, particularly at it's resonant frequency and be felt in the car at certain speeds, generating customer pleasability issues, erratic tire wear and/or durability concerns".

The kid looks blankly at the engineer and says "yeah. Cause if I don't it'll wobble".

:lol:

K

Re: Why a 2 piece driveshaft?
 

I had always thougth it was also a clearance issue. The 2-pc has the primary shaft level to the chassis and the secondary tilts downward to the rear axle. This set up would have more clearance than a 1-pc shaft that tilts downward from the tranny to the rear axle. If the wheelbase is small enough the difference in clearance is negligible, but as the wheel base increases it becomes a ground clearance issue with the driveshaft. Aside from what has been mentioned in previous posts. I could be wrong, it wouldn't be the first time.
Just my $0.02
Dano

Re: Why a 2 piece driveshaft?
 

I had my carrier bearing tear off the frame a few years ago; broke a u-joint & dropped the driveshaft. Had to have new "ears" welded on and a carrier bearing pressed on. Here is the shop that did it: http://www.samwinermotors.com/ excellent shop and very reasonable.

Re: Why a 2 piece driveshaft?
 

I may be understanding you wrong but,

That doesn't make any sense to me. If i have the same trans as you but i have 5.14's in the rear the drive shaft spins a lot faster than it would at as say a 2.73 ratio. I had a 3/4 ton 67 with 5.14 posi in rear and it had two pieces. It has to turn 5 times around before the tires turns around once. hence the high rpm at a low speed.

Larger engines don't have anything to do with top speed. unless you need tons of power to get to a ridiculous speed. your last gear in your trans is 1:1 unless its an overdrive. Gears in the differential more than anything allow for a higher top speed.

Also i was under the impression that it was the short beds that got the one piece. i could be wrong.

Re: Why a 2 piece driveshaft?
 

That makes some sense finally raycow. Thanks...

Re: Why a 2 piece driveshaft?
 

Stitch, many cars pulled camping trailers etc. that exceeded 1000 pounds. They put on Reese hitches and overload springs often to pull their camping trailers.

Re: Why a 2 piece driveshaft?
 

There you go right there, if an engineer were to do his critical speed calculations based on a vehicle speed of 60mph that 5.14 ratio may spin a 1 piece driveline at or near its critical speed, that same 1 piece driveline on the 2.73 ratio rear end @ 60 mph maybe well below its critical speed. Based on that logic the dive line on the 5.14 ratio rear end should be a 2 piece, larger diameter or different material.

.
Often times vehicles with smaller lower torque/hp engines were equip with lower gear ratios to compensate for the lack of power.

Re: Why a 2 piece driveshaft?
 

yes I know that, but the truck was engineered to do it..
at ride height or bumber drag'n.

tail drag'n a wagon and tow'n kills ujoints,, and gives a stock 1 piece tube a slight twist to it..
draw a line on a driveshaft in a wagon then tow 1500 miles and look at the line again.. unless you drove like a granma, it's got a slight twist to it..
even light power over wet r/r tracks will do it..
once it starts it only gets worse..

Re: Why a 2 piece driveshaft?
 

This thread has been long over due, and I appreciate such an excellent explanation to why some have different setups.

Sounds like the 2 piece is the better all around choice, as the 1 piece were used on trucks with lower gearing (Probably because it was cost effective).

2 piece was used for trucks that had higher gearing to keep critical mass down.

Do I have this correct?
s/t

Re: Why a 2 piece driveshaft?
 

Mr. Chevy (or anyone), let me know what you find out. I'm in the same predicament. I just converted my long bed coild spring chasis C-10 to a short bed. I'm planing to keep everything else original 250 6 Cyl, 3 manual trans. But I need to resolve the driveshaft issue. My plan was to look in a bone yard for a one-piece driveshaft from a 67-72 6cyl, three on the tree tranny. Any suggestions? My other option was to have one custom built...suggestions?

Re: Why a 2 piece driveshaft?
 

One piece ds' are always a larger diameter to compensate.

I have a 72 SWB step. I swapped in a 700r4. I slipped an old yoke I had into the trans, measured from where the middle of the front yoke would be to the where the middle of the rear yoke would be and got 55 1/2" at ride height. A few weeks back, I came across a Craigslist ad from someone selling a driveshaft out of an 85 Chevy SWB... It was 55 1/2" center to center as well.

Re: Why a 2 piece driveshaft?
 

Sorry to high jack the thread here, but I'm curious; How did you convert from long bed to short? New frame or cut the old one? Also, do you know the length difference between the frames?

Re: Why a 2 piece driveshaft?
 

I've allways wondered why people want to go with one peice shafts. I have had 5 of these trucks over the years and only had one carrier bearing go bad. There plenty strong .My truck now has the stock two-peice and I run this truck at the track. 4500lbs, 180 shot of nos and no problems. I just dont see the advantages of a one-peice. my .02 .

Re: Why a 2 piece driveshaft?
 

Personally, I am only going to a one piece because of a trans swap and the one piece was $35