75 GMC C15 rear u joint too small

[hillytim69]

I am converting my stepside to a th-350 with a 1 pc driveshaft that i got from another '75 Chev swb donor vehicle. My truck originally came with the sm-465 4 spd with a 2 pc shaft with a center carrier bearing. I got the th-350 in and put new precision 369 u joints on my 1 pc shaft. Then when I tried to put the shaft on the rear axle yoke, I found my rear ujoint to be at least 1/4 inch too narrow. The rear axle yoke on my truck is bigger than from the donor truck i got the shaft from. I'm not surprised because everything on my truck is heavy duty for a half ton. i just need advice on what to do. Do i have the driveshaft modified to fit the bigger joint or replace the yoke on the rear end with the smaller one ( if i can find one at the junkyard). Would the pinion depth be affected if I remove and reinstall a different yoke? Or is there a special u joint for this situation? i can't imagine a ujoint that is wider one way than the other, seems like it would be unbalanced. I'm sure this is a common question on here but I couldn't find quite the exact info I needed on my searches. I sure am getting antsy to get this thing ready to fire up for the first time and any help i can get to point me in the right direction is really appreciated.

[Driveway Dreams]

You need an adaptive u-joint. I got one for my truck. I will try to find the part number I used. I found the info in the engine & drivetrain board on here.

[hillytim69]

thanks, I just stumbled across a thread similiar, is the precision 348 the part I need? Still seems odd to me that a u joint would be wider one way than the other, I suppose I'll need to have the driveshaft balanced for sure.

[Driveway Dreams]

I got mine from my local parts store. Gave them a Spicer part number and had them cross reference it. I needed one because my truck had a 10 bolt and when I put the 12 bolt in the flanges were different. I don't think you will have a ballance problem with it.

[hillytim69]

For anyone else who has this problem, there are 2 different Precision brand conversion u joints. The part number I needed is #353, it is a 1310 to 1330 conversion ujoint. It measures 3 1/4" cap to cap one way and 3 5/8" the other way and all cap diameters are 1 1/16". The #348 joint ( I mistakenly bought) is a 1310 to 1350 conversion and measurements are the same except 2 of the cap diameters are the much larger 1350 style. I know this because I got the 348 and the large caps dont fit my rear axle yoke. Gonna go get the 353 and finally get this driveshaft installed. Hope this helps others...

[asphaltburner]

Yo! Glad you guys found what you needed! Northern Colorado Driveline supplied me with my driveshafts, but I got quite an education when it came time to order them!
Amazing the choices that are available out there for yokes (spline counts, styles, duty strengths) and U-joints (width combinations, cap sizes and combinations, and duty strengths)! Just amazing, and all those guys do, so they KNOW their stuff.
They set me up with 32 spline output from my NP205 front and rear with the heavy duty yokes, and appropriate U-joints for the axle ends. Magnificent!
Cool that we have all these great sources here in Colorado! Off Road Design (who built my machined, twin-stick NP205) is in Carbondale, CO!
Have fun!
Todd.