Drive shaft replacement

[vgrn]

Need new front and rear drive shafts. Anyone know which ones and size I need? 1977 k15 small block 350 5.7 v8, automatic transmission, 10.5” 14 bolt gm corporate rear full floater rear axle, np203 transfer case, 8’ bed

 

[Bextreme04]

You don't have any driveshaft currently? Which trans do you have? A TH400 is a different length than a TH350

 

[vgrn]

it’s a TH350 trans and I currently have drive shafts on it. The mechanic said that the velocity on the front one is completely shot

 

[Travlr]

Well rather than starting a new thread I'll scab onto this one. It appears the OP never got their answer and it's been a while so I doubt they will mind.

I have a '78 K20 that has a lot of slop in the front drive shaft. It looks like it's been repaired on the farm and really needs to be replaced. I went to the local wrecking yard and they sold me one that looks very similar for $45, and I'd like to know if there are any concerns with replacing the old one with the other...

In the pic (shaft from truck closest in the pic) you can see that they measure out the same length and the two ends are the same, but there is a difference in the tube lengths. You can see the difference where I placed a putty knife next to them. As said, I doubt the one from the truck is exactly as originally manufactured as there are funky welds and no balancing weights on it. The '78 isn't lifted or lowered, stock height, so that isn't a concern.

Should I use the shaft from the wrecking yard? Were there any differences that I should be aware of?

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[SquareRoot]

Word of advice from experience. It's probably all junk. This is one area where you don't want to hobble old used crap together to save a few bucks. Go to a reputable driveshaft shop and have a new one with new parts made. One and done. I paid $800 for all new HD shafts ( front and rear ) with 1350 spicers CV's.
To your point: the top shaft is almost collapsed. If you install a shaft with too little travel and hit a bump that causes it to bottom out, you will instantly destroy your transfer case. The $$$ that will cost you will pare in comparison to having a new shaft built from the beginning.

 

[Travlr]

Word of advice from experience. It's probably all junk. This is one area where you don't want to hobble old used crap together to save a few bucks. Go to a reputable driveshaft shop and have a new one with new parts made. One and done. I paid $800 for all new HD shafts ( front and rear ) with 1350 spicers CV's.
To your point: the top shaft is almost collapsed. If you install a shaft with too little travel and hit a bump that causes it to bottom out, you will instantly destroy your transfer case. The $$$ that will cost you will pare in comparison to having a new shaft built from the beginning.

Appreciate the response but any kind of driveshaft shop is over a hundred miles away. Both shafts are fully collapsed and measure the same (29 1/2) u-joint to u-joint.

Is there a difference between the shafts used for a 350 and 400 trans? Some of the listings I'm finding use the u-joint to u-joint measurement at 29 1/2 for a 350 and then there is one that says it fits a 400 and is 32 1/2... but it doesn't say if it is measured from the u-joint to u-joint or u-joint to flange, which my shafts both measure both dimensions depending on how you measure them.

And I found a video that says shafts can be measured four different ways, two of which I just described.
I suspect they are all the same...

 

[Ricko1966]

Since you don't know if that's the original drive shaft or if it's the correct length. With the truck sitting on the ground measure from flange to center of where the ujoint should be. Now check that length against your new driveshaft your drive shaft should be that length plus and minus for room to move when compressed and extended. If it physically bolts up,and is correct length,I'd check the ujoints and run it. I would change the Ujoints but I think that might be out of your skill set

 

[Travlr]

Since you don't know if that's the original drive shaft or if it's the correct length. With the truck sitting on the ground measure from flange to center of where the ujoint should be. Now check that length against your new driveshaft your drive shaft should be that length plus and minus for room to move when compressed and extended. If it physically bolts up,and is correct length,I'd check the ujoints and run it. I would change the Ujoints but I think that might be out of your skill set

LOL... well I appreciate your lack of confidence in my skill set.

And so far nobody has answered the question if all the drive shafts are the same length regardless of transmission.

 

[Ricko1966]

Im sorry I should have worded that as I don't your skill set. I would just measure what I needed and go from there. When I put engines and transmissions into cars they never came in that's how I do it, I measure for what I need, just don't forget to leave room for extension and compression.

 

[SquareRoot]

And so far nobody has answered the question if all the drive shafts are the same length regardless of transmission.

No. Further, they can be different with the same transmission.

 

[75gmck25]

I’d probably use the bottom one, and install all new sealed u-joints. Use sealed u-joints because everybody forgets to lube the type with zerks on them. Then lube the slip joint and make sure it slides in and out smoothly.

 

[75gmck25]

When I lived in San Antonio there was a local driveshaft shop, and I just has them rebuild my front driveshaft. That one lasted about 18 years before one of the u-joints rusted out and fell apart. Replaced all the joints a few years ago and it’s still working fine.