Differences in driveline length between 10&12 bolts?

[Jabes1]

I'm curious if there is any difference in drive line length between 10 and 12 bolt rearends? I guess what my question really is does my driveline need to be lengthened or shortened if I go from a 12bolt to 10bolt and vise versa...

I'm building my truck to cruise on the interstate, and I've located a rearend that's a 10bolt with 2.73's. I don't want to go through the hassle or expense of setting up a rearend with different gears just to find out its not suited for what I want and then have to redo everything. Swapping rearends is far easier and cost effective than changing gears several times...

[Tx Firefighter]

I've never needed to modify length, but the u joints are different. You'll need a conversion u joint available from any parts store. It adapts the two different era parts together by having two different sized dimensions.



I'm currently running the opposite combination in my 78 truck. A driveshaft out of an 87 model truck which had a 10 bolt rearend with the 78 model 12 bolt rearend. The conversion u joint makes it all work.

By the way, a non overdrive trans, 2.73 gears and 28 inch tall tires is an outstanding combination for highway cruising. I daily drove that exact combo for a lot of years in my 83 stepside. It made my 40 mile freeway commute a pleasure.

[Jabes1]

Thank you TXFirefighter. Ill have to look into if they make a 1350 to 1330 conversion U-joint. I wonder if the yoke is interchageable from my 12bolt to the 10bolt... I'd like to keep my 1350's.

[Jabes1]

I have a Gear Vendor behind my TH400 with 29.74" tires, so Im not sure if its going to be too high of a gear. In theory, with my Tri-Y's and Tuned Port it shouldn't lug the engine too much and be a nice boost in MPG's.

[LostMy65]

Does anyone know if at a certain year, GM trucks went to either metric u-joints or u-joint bolts and nuts?

[ElGracho]

Originally Posted by Tx Firefighter

I've never needed to modify length, but the u joints are different....

Some 12 bolts have 3r yokes like a 10 bolt. I have one I just swapped into my 85. I think it came from a 1979 or 1980 suburban. 3.40 posi...

I didn't change anything with the driveshaft but I do think it was out of the trans about 1/4" more than it was with the 10 bolt.

[LostMy65]

Originally Posted by LostMy65

Does anyone know if at a certain year, GM trucks went to either metric u-joints or u-joint bolts and nuts?

.
I've spent the last few days reading up on driveshafts and u-joints.
My concern was knowing which driveshafts were compatible with C10 trucks. It appears from helpful posts from members here that pretty much any GM model vehicle driveline will work - although it may require a combination u-joint. 1310, 1330, etc.
Now my only question that remains is:
Did GM ever switch to metric u-joints?
I have searched and searched, and as far as I can tell; No they did not.