1/2 to 3/4 ton driveshaft

[GreenMystChevy]

What driveshaft should I use beinig that my transfer case has the small u-joints yet the axles have the larger ones. I can't use my existing driveshaft unless I use hybrid u-joints. I thought that 3/4 tons had something like a 4" diameter shaft. Is this better and will it last longer?

I am putting together my '72 and I have put '75 3/4 ton axles under it. I made sure to have 3/4 ton axles under there because I am going to be running 38"s and maybe bigger later on and I don't want to be replacing things all that often, including u-joints snapping. I am running a Rockwell 221 transfer case.

What is going to be my most efficient way to go as far as quality and price? Completely new shaft custom made, different end yolk on my existing shaft to accept the 3/4 ton u-joint, different bottom shaft (the longer driveshaft that slips onto the little one bolted to the transfer case), etc. Thanks guys.

[LeRoy]

I first used the conversion u-joint then came across a rebuilt driveling from a 72 3/4 4x4 longbox. I had it shortened for around $50. It's cheap to shorten them but expensive to lenghten. As for the t-case end it was the same u-joint as the 3/4 ton but the 14 bolt is bigger then the 12 bolt. If you think about it 3/4 tons came with the NP205 to. If anything you might get away with a bigger slip yoke on the t-case end.

[GreenMystChevy]

I think I'm starting to understand it now.
All t-cases have the same u-joint size it's just the axle that changes?
Should my plan of attack be to get a driveshaft from a 3/4 ton and get it lengthened for the 8" lift?

[DaHateTank]

hate to rain on the old parade...BUT...

All T-cases do NOT have the same U-joint size. Even all NP205s do NOT have the same U-joint size.

I broke the yoke off of my 205, a couple of months ago, when I unexpectedly hooked up on pavement. I had a couple of 205s outta 3/4 ton PUs in the shed. The 3/4 ton yoke took the bigger 1350 joints.

Fortunately, I also had a driveshaft, that I got in the same deal, with a 3/4 ton slip yoke. The 3/4 ton yoke slid right on to the splines on my driveshaft. I now have a 3/4 ton T-case and a 12 bolt diff.

That might cause vibration issues, I guess, but my driveshaft is pretty worn out anyway Anyway you should be able to get a new end for your shaft, that will accept the larger joint, or have a shaft made that will solve your problem.

If you currently have a fairly new shaft, in good shape, and don't want to mess with the balance, then the conversion joints are an option. Personally, Im not a big fan of those, 'cause they're not any stronger than the smaller joints, and cost more to replace (which my junk requires fairly often...LOL)

-M

[GreenMystChevy]

Thanks for that, it kinda cleared things up.

So a 3/4 ton shaft will slip onto the part that bolts to the t-case even if that is for a 1/2 ton?
So my best bet would be to get a 3/4 ton shaft and have it lengthened for the lift. I would then have a 1/2 u-joint at the t-case and a 3/4 ton u-joint at the axle?

Nothing like learning things for the first time.

[DaHateTank]

Originally posted by GreenMystChevy
Thanks for that, it kinda cleared things up.

So a 3/4 ton shaft will slip onto the part that bolts to the t-case even if that is for a 1/2 ton?

Mine does. Im not sure if they're all that way (In fact, I kinda doubt it) Kinda seems that it means the 3/4 ton shaft isn't any stronger than the 1/2 ton shaft, IMO. I am sure you can buy a bigger slip coupling, but Im not sure who used what, and when. You'll need to check, when you find anything, I 'spose...

By 'part that bolts to the T-case', Im assuming you mean the shorter part of the DS... Ive seen 'em put on either way. Haven't really heard any convincing arguments for which way is 'right'

Originally posted by GreenMystChevy
So my best bet would be to get a 3/4 ton shaft and have it lengthened for the lift. I would then have a 1/2 u-joint at the t-case and a 3/4 ton u-joint at the axle?

If you can find a 'good' 3/4 ton shaft, and it is the same, that should work. In my experience, the splined coupling wears pretty fast, so it might be just as easy/wise to have a shaft made... Not sure how much they charge to lengthen a shaft, but it would seem, to me, that they would have to turn (lathe) the pieces they could use, off of the old shaft, and weld them to a new piece of tubing. If either end is junk, it might cost almost as much as a new shaft... (my NEW front was $250+ IIRC, rear was just as much???)

An even better idea, may be to get a T-case yoke, off of a 3/4 ton, with the same t-case, (or a yoke that takes the larger joint, and fits your transfer), and just use a 3/4 ton DS. That way you have the larger, and stronger, joints at both ends...

Originally posted by GreenMystChevy
Nothing like learning things for the first time.

Better than having to learn them over and over!!! That would mean you were stupid... I work with some guys like that...LOL!!

Seriously, I wouldn't know any of this stuff, if I hadn't had a coupla NP205s laying out in the shed, that I got for the right $$$. One advantage of having a buncha 'junk' laying around, I guess!!!

best of luck
-Marty

[GreenMystChevy]

Marty: I really appreciate the help. I wanted to make sure I knew what I was talking about when I called the driveline shop to talk prices. Ill ask them flat out what is going to be the cheapest route.

I would love to find a transfer 3/4 ton transfer case yolk but I have a feeling with a Rockwell 221, I just might be S.O.L.

Thanks for the time and if I find anything all too interesting out I'll let you know, just for future info.


Thanks guys for your help!