Why a 2 piece driveshaft?

[Coley]

Wow, interesting thread.
In addition to the very important 'critical speed' issue is the ability to work around this speed....of which they are indeed ways.
For instance, if you went with a (less desireable) solid steel shaft you would very quickly find you couldn't rotate it as fast as you could a larger diameter hollow shaft due to its concentrated (central) mass wanting to initially bend at both rest conditions and at higher speeds.....and definitely quicker to approach this condition than the hollow one.
That is why you find most (all?) driveshafts, that are subject to high speeds, made of a hollow (larger diameter) tube material that is inherently stiffer over its length than a solid steel smaller diameter shaft over the same length.
Thus a great result of this is the ability for a large diameter tube to successfully deliver torque with a minimal amount of axial twist relative to its length....nice to have.
A lot of folks would really be surprised to see just how thin the material on a high hp driveshaft, or any typical driveshaft is....lol. Its actually, physically a fairly light part relative to its length and this is achieved by increasing the diameter which keeps it stiff while allowing excellent torque transmission characteristics.
If you want to have some fun....make a driveshaft out of solid 1-1/4"ø steel and wind up the vehicle on a hoist to say....4500 rpm, and watch the driveshaft....(from behind a screen or shield)...lol.
Interesting discussion....lets keep it going!
All Good
Coley

[Saloonwarrior]

Originally Posted by grs

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.

I was told by Sadler Powertrain to install yoke into transmission until it bottoms out, measure from center of yoke holes to center of rear housing yoke holes then subtract 1 1/4" for proper clearance.

[70STOVEBOLT]

Originally Posted by Saloonwarrior

I was told by Sadler Powertrain to install yoke into transmission until it bottoms out, measure from center of yoke holes to center of rear housing yoke holes then subtract 1 1/4" for proper clearance.

This IS the correct way to do it.

[70STOVEBOLT]

Originally Posted by Mike_The_Grad

I had forgotten I was subbed to this thread, how strange I was notified of an update to this thread at the same time I'm facing a 2 piece driveshaft dilemma on my '72 custom/10 LWB with factory overload rear leaf suspension. I had removed the driveshaft a couple years ago to rebuild the 350 sbc, I had to remove the actual center bearing support bracket from the frame in order to remove the driveshaft. Now I can't remember which of the two 4-bolt bracket mounting locations (heightwise) is the correct one for my vehicle. I do have the factory assembly manual and it does not define which of the two is correct. It does differentiate between the two based on RPO#'s but only for 1968 vehicles, with no mention anywhere else in the entire book of any other production years.
Picture for reference and clarification on which holes I'm referring to.

Look on the other side of the crossmember. Can you see where the washers/nuts/bolts were on that side? I don't know how these mount up as I have never had one with a 2-pc shaft. I do know that my 70 came with a 250/3OTT from the factory, coil springs, one-piece driveshaft. I put a 402/TH400 in it and had a local driveline shop shorten and balance it, put new u-joints on it, and I have had it up to 100 mph - smooth as silk.

[Mike_The_Grad]

Originally Posted by 70STOVEBOLT

Look on the other side of the crossmember. Can you see where the washers/nuts/bolts were on that side? I don't know how these mount up as I have never had one with a 2-pc shaft. I do know that my 70 came with a 250/3OTT from the factory, coil springs, one-piece driveshaft. I put a 402/TH400 in it and had a local driveline shop shorten and balance it, put new u-joints on it, and I have had it up to 100 mph - smooth as silk.

I examined both locations pretty well,and was unable to get a distinct indication of where it was originally mounted,mostly because of all the old crud and oil built up on the frontside of the crossmember. But I went ahead and mounted it to the lower of the two mounting locations. I threw the u joint that is connected to the pinion of the differential back in December, which I believe was due to my failure to replace the spring clips over the end caps where the two straps secured the joint to the pinion. In addition to maybe not having the driveshaft in phase with the other components(180° out). So I replaced the joint and changed the driveshaft relation 180° installed the retaining clips,lol, and now I've got almost 10k miles on it,and had it up to about 115 m.p.h.!! My carrier bearing is shot though and I'm pretty sure the other u joints have seen better days. So as soon as I get the money,I'll be replacing all the u joints, the carrier bearing, and rebalancing the driveshaft at a local very reputable driveline shop. Coast Driveline out of Ventura, CA.