2-Piece Shaft swap into a K20 Longbed

Disclaimer: Links on this page pointing to Amazon, eBay and other sites may include affiliate code. If you click them and make a purchase, we may earn a small commission.

SquareRoot

Full Access Member
Joined
Mar 18, 2017
Posts
4,188
Reaction score
7,998
Location
Arizona
First Name
Mike
Truck Year
85
Truck Model
K20
Engine Size
350
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
You must be registered for see images attach




You must be registered for see images attach
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.
 

Frankenchevy

Proverbs 16:18
Joined
Jan 3, 2018
Posts
6,076
Reaction score
7,743
Location
USA
First Name
Jeremy
Truck Year
Square
Truck Model
CUCV
Engine Size
Small
If you decide to stay 1-piece and go aluminum, I’ve used these guys and they do good work.


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

Full Access Member
Joined
Mar 18, 2017
Posts
4,188
Reaction score
7,998
Location
Arizona
First Name
Mike
Truck Year
85
Truck Model
K20
Engine Size
350
If you decide to stay 1-piece and go aluminum, I’ve used these guys and they do good work.


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

Proverbs 16:18
Joined
Jan 3, 2018
Posts
6,076
Reaction score
7,743
Location
USA
First Name
Jeremy
Truck Year
Square
Truck Model
CUCV
Engine Size
Small
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

Member
Joined
Jun 26, 2017
Posts
45
Reaction score
21
Location
ME
First Name
Ben
Truck Year
1976
Truck Model
K20
Engine Size
350
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

Full Access Member
Joined
Mar 18, 2017
Posts
4,188
Reaction score
7,998
Location
Arizona
First Name
Mike
Truck Year
85
Truck Model
K20
Engine Size
350
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.
 

Attachments

  • IMG_20230416_162028766_HDR.jpg
    IMG_20230416_162028766_HDR.jpg
    122.9 KB · Views: 48

Strick

Full Access Member
Joined
Nov 25, 2020
Posts
1,340
Reaction score
3,273
Location
Dunn, NC
First Name
Harold
Truck Year
1979
Truck Model
C20 Crew
Engine Size
350
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

Full Access Member
Joined
Mar 18, 2017
Posts
4,188
Reaction score
7,998
Location
Arizona
First Name
Mike
Truck Year
85
Truck Model
K20
Engine Size
350
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.
 

Attachments

  • IMG_20230519_160408301.jpg
    IMG_20230519_160408301.jpg
    74.2 KB · Views: 49
  • IMG_20230505_115759423.jpg
    IMG_20230505_115759423.jpg
    87.8 KB · Views: 49
  • IMG_20230519_154544072.jpg
    IMG_20230519_154544072.jpg
    56.3 KB · Views: 56
  • IMG_20230517_162420981_HDR.jpg
    IMG_20230517_162420981_HDR.jpg
    75 KB · Views: 48
  • IMG_20230519_154529703.jpg
    IMG_20230519_154529703.jpg
    61 KB · Views: 52

SquareRoot

Full Access Member
Joined
Mar 18, 2017
Posts
4,188
Reaction score
7,998
Location
Arizona
First Name
Mike
Truck Year
85
Truck Model
K20
Engine Size
350
A few more pics...
 

Attachments

  • IMG_20230519_171427702.jpg
    IMG_20230519_171427702.jpg
    91.3 KB · Views: 56
  • IMG_20230519_171424425.jpg
    IMG_20230519_171424425.jpg
    83.6 KB · Views: 53
  • IMG_20230519_154641650_HDR.jpg
    IMG_20230519_154641650_HDR.jpg
    105.3 KB · Views: 48
  • IMG_20230519_171414094.jpg
    IMG_20230519_171414094.jpg
    95.6 KB · Views: 50
  • IMG_20230519_171357959.jpg
    IMG_20230519_171357959.jpg
    82.3 KB · Views: 49

SquareRoot

Full Access Member
Joined
Mar 18, 2017
Posts
4,188
Reaction score
7,998
Location
Arizona
First Name
Mike
Truck Year
85
Truck Model
K20
Engine Size
350
There's a lot going on in that last pic above. Can anyone guess what their looking at?
 

Latest posts

Forum statistics

Threads
44,066
Posts
948,698
Members
36,134
Latest member
gtewolf79
Top