2-Piece Shaft swap into a K20 Longbed

[SquareRoot]

I never thought I would ever hear anyone say that.

One thing to consider is your antipated vehicle top speed. The shaft critical RPM is a function of shaft material, diameter, wall thickness, vehicle speed, rear axle ratio, tire diameter, and maybe a few more variables.

The shaft was designed to handle some predetermined top speed, typically 106mph or 120mph. So one way to control the shaft rpm is to slow the F down.

You might ask yourself if you ever intend on going that fast in this thing, and if not, that might be a consideration that moves you back to a one piece if you are on the fence.

(I always do a one piece if I there is any way to get away with it).

K

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Thanks for chiming in. I see your point and speed wont be an issue in this case. I was reading several offroad sites that were unanimously frowning on the 1 piece due mostly to clearance issues.

 

[SquareRoot]

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[Frankenchevy]

If you decide to stay 1-piece and go aluminum, I’ve used these guys and they do good work.

http://www.driveshaftspecialist.com/

Pretty reasonable considering the construction. Mine has upgraded 1480 u-joints, 1/8” wall, etc. It’s stout. About $1000+shipping, iirc. Maybe $1300 to my door.

 

[SquareRoot]

If you decide to stay 1-piece and go aluminum, I’ve used these guys and they do good work.

http://www.driveshaftspecialist.com/

Pretty reasonable considering the construction. Mine has upgraded 1480 u-joints, 1/8” wall, etc. It’s stout. About $1000+shipping, iirc. Maybe $1300 to my door.

Thanks. I was looking at their website. Are you running the 208 t-case? Did you opt for the double CV joint on Franken?

 

[Frankenchevy]

Thanks. I was looking at their website. Are you running the 208 t-case? Did you opt for the double CV joint on Franken?

I went aluminum on my older CCLB Cummins to eliminate the two piece. On the square I went with steel, but I did have it lengthened as well. The factory stick out on the slip yoke was over 3”. Now it’s closer to 1” from bottoming out.

Still running the 208 in that truck. The round pattern 205s are tough to find. I’ll likely end up with an aftermarket 3:1 T-case in that truck. The 208 is probably good enough to live quite a while behind my relatively low hp engine, though.

The nice part about a flanged T-case is the ability to run a driveline parking/e-brake. That frees you up to run any caliper in the rear. I don’t think doing an SYE on a 208 would be worth it for the same benefit.

 

[bft305]

I have a k20 long bed lifted 6” with a th350 and just swapped in a np205 about a year ago. It has a np203 and the 205 was shorts by a good amount. Had to have both driveshafts resized. I was just under the max length the drive shop guy said, I think he said 70” and I was like 68” (can’t remember exactly). Either way he made me a new one and it works great! Maybe you should call around and see what the shop will do in terms of max length.

 

[SquareRoot]

I have discovered since starting this thread that most places that don't (won't) build the 63" + shafts is because they don't have the capability to high speed balance them and therefore won't sell them. That was the response I got from Denny's and a few other well known places. However, I also learned I should use a CV, even at the shallow angles I have. It will run smoother and last longer. Those are generally almost a foot long which doesn't count towards the shaft length. And like @Keith Seymore says, length is only one variable in critical rpm. The place that @Frankenchevy mentioned can build me just what I need so I'll be ordering one from them as soon as I swap the trans/T-case so I can get accurate measurements. I just wrapped up a complete teardown, rebuild and twin stick conversion this weekend. Now I'm dreading heaving that #350 beast into place.

 

[Strick]

I have discovered since starting this thread that most places that don't (won't) build the 63" + shafts is because they don't have the capability to high speed balance them and therefore won't sell them.

I have a 79 K20 that I'm currently working on. SM465/NP205 fixed yoke and 2 piece shaft. The marine has killed a few center bearings already because the front half-shaft is too short with the 6" lift. I just spoke with him yesterday afternoon and told him it was going to be awful expensive to do a 1 piece in the truck due to the length of it. You have 63 and my rough (laying in the field) measurement was 62. I know a 1 piece was used in 80 but they were slip yoke and not fixed. I don't think speed is the issue with him because this thing is a lifted beast with 37's.
Keep us informed of what you find out. Thanks.

Strickland

 

[SquareRoot]

UPDATE: Been busy lately but getting things done on the truck. Got the rebuilt NV4500 and 205 T case installed. I discovered I have a very reputable driveline shop here in town.
Got a brand new front shaft built and installed. I also got a brand new rear shaft built. I opted for the 1350 series Double Carden (CV) versus a u-joint. The things a beast! We couldn't source the proper flange so we opted for the "Jeep" style CV yoke. The CV bolts directly to the yoke with caps. No U-bolts or straps. Very clean setup. The shaft length from center to center ended up being 62.5 inches, FYI.
So with all new parts including Spicer 1350 all around the guy charged me $775. I was very happy with that. I gave him 8 $100 bills and told him to keep the change. I realized afterwards that I need to adjust my pinion angle since with CV's you point the pinion shaft directly at the CV versus the 3 degree parallels/offset way a u-joint works. A call to ORD and $40 later they showed up yesterday.

 

[SquareRoot]

A few more pics...

 

[SquareRoot]

There's a lot going on in that last pic above. Can anyone guess what their looking at?

 

[Catbox]

I am a 2wd guy currently, so to me it is stuff and things.
But it looks damn good.