I'll try this again....
 

Hello all, happy new year. I have a 79 swb 2wd half ton. It has a 2 piece drive shaft as far as I can tell its factory. Ever heard of such a thing? My problem is I cant switch to a 1 piece bc my th400 has the bolt on yoke. so I'm stuck with a 2pc????

Re: I'll try this again....
 

Happy new year! Long beds with a 400 (bolt on yoke) came with 2 piece drive shaft with a carrier bearing. Short beds came with a 1 piece drive shaft with a slip joint. You just need to find one or get a new one made. Here's what it should look like:

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Thanks Mr chevy, that is what I need. still wondering why I have a 2 pc. it even has the carrier mount riveted in place. Weird......

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That is weird. I have never seen a short wheel base truck with a 2 piece from the factory. Any evidence of the truck having been shortened? I have seen long wheel base trucks with factory original 1 piece drive shafts (pretty sure they were all th350 with slip yoke).

Mike

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no, I cant see anywhere the frame was cut and welded BTW where did you find the pic of that shaft, I will probably go aftermarket for one. don't think I would have any luck at a salvage yard

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I just did a quick google search for a picture. Denny's does make good shafts though. I ran one in my rock crawler and never had a problem with it.

http://www.dennysdriveshaft.com/


Mike

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My swb 78 Big 10 454/400 came from factory with a 2-piece driveshaft.

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My 1985 SWB C10 with a 4.3 and SM465 4 speed also came with a two piece from the factory.

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[QUOTE=Mr.Chevy4x4;7811284]That is weird. I have never seen a short wheel base truck with a 2 piece from the factory. Any evidence of the truck having been shortened? I have seen long wheel base trucks with factory original 1 piece drive shafts (pretty sure they were all th350 with slip yoke).

Mike>My 77 Shortbed Chevy Sport with Muncie 465 has the 2 piece driveshaft from the factory. (Picture below) BTW:Center Bearing Support is still available from GM. Larry:chevy:

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Wow thanks guys. never knew gm made them w/ 2pc. Big 10, good to see one behind a 454. guess I'll order some more parts

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One piece vs two piece is determined by the shaft critical speed (the rpm at which the shaft starts to bend).

Inputs to critical speed calculations include: wheelbase, shaft overall length (a function of wheelbase and also transmission length), shaft material, tube diameter and wall thickness, rear axle ratio, tire diameter (and speed rating) and anticipated vehicle top speed, as well as any unforeseen destructive system resonances discovered during physical testing.

Changing any of those can make the difference between a particular model getting a one piece or a two piece shaft.

I could envision a small displacement 2wd lwb truck getting a one piece shaft, especially with a lower numerical rear axle ratio, due to a potentially lower top speed and the slower shaft rpm due to the axle ratio. Higher horsepower engines, allowing a higher vehicle top speed, might drive the design into a two piece shaft (or a one piece shaft of more exotic materials). Speed limiting the vehicle, through fuel cutoff or ignition rpm limiting, or releasing a lower speed rated tire, could put you back down in the range when a one piece shaft would be acceptable.

K

http://67-72chevytrucks.com/vboard/s...light=critical
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MY 78 half ton step side 5.7L with the 8 leaf rear spring pack and sm465 came factory with a 2pc driveshaft. I swapped to a 1pc from a th350 truck when I put the M20 trans in after cutting it to fit.

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Wow. Learn something new every day. I've been around these trucks my entire life and never seen a short wheel base with 2 piece shaft. Had several already state on here that their trucks have them. Feel like I've been living under a rock or something! :) I stand corrected.

To the OP: I would still replace it with a quality 1 piece considering your performance application. Less points of failure.

Mike

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You can just unbolt the yoke from the TH400 and use a slip yoke in it's place. It's the usual 32 spline.

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I have read somewhere that it shouldn't be done

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What was the reason? I did it on my truck a couple years ago and it works fine.

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I've removed a fixed yoke and ran a slip yoke for years as well with no issues

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The output shaft for a bolt on yoke 400 has a ridge just past the splines that the slip yoke can bottom out on causing internal damage. If you're going to do this the ridge should be removed.

You can see here where the slip yoke made contact.

Mike

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Makes sense. I remember when I put mine together that the yoke didn't slide in as far as I thought it should have. But it works fine for my application, it really doesn't need much slip travel (stock height shortbed).