What's new
CK5
Register an account today to become a member! Once signed in, you'll be able to participate on this site by adding your own topics and posts, as well as connect with other members.

12 Bolt Tube Size?

evolve991

evolve991

Resident Problem Child
Joined
Nov 1, 2010
Posts
716
Reaction score
24
Location
Lordsburg,New Mexico
So I just got my DIY Spring Plates for my GM Corp 10 this week. And U bolts. Today I bought a rear out of a 76 K10 1/2 ton. Assumed it was a Corp 10....it's a 12 bolt....how screwed am I on the plates and bolts? And all new brake pads and springs for that matter? :confused:
 
OK I'm sifting thru tons of info on 10 and 12 bolts and not finding exactly what I need to know. I'd be out in the dark with a flashlight measuring it but there's a wicked thunderstorm having a blast in my area. Anyone know the differences in axle thickness,etc on 10s and 12s other than the 8.5 and 8.875 rings?


PS: IF a had WANTED a 12 bolt I'd have never FOUND one :doah:
 
I'm no expert,but I think all 1/2 ton axles are the same diameter and the spring plates are the same size...as for the brakes I think they go by the GVW rating ,you could probably swap the backing plates to use your new shoes and hardware on the 12 bolt,if the bolt pattern is the same..the repair bearings should be available for both axles also...
 
Thanks Diesel:waytogo: I just found the brakes on NAPA and they're basically the same range and size.

But...just thought of another potential problem....drive shaft....I bought the one that went with the 12 bolt just to help the guy out with a little more cash...now I'm thinking it was a good idea...I believe the 400 spline and later NP 241/700r4 splines are the same...sorry guys just thinking out loud and hoping for input...when I thought this was a 10 bolt there were less questions.....

Or am I headed for a bastard joint search?
 
brake backing plates swap if brakes not correct size .

stay the HELL away from repair bearings . they suck these days .

rear yoke can be swaped from 10 bolt to 12 bolt for direct fit if not the same size u-joint.
 
TH400 has 32 splines on the output shaft,the TH350 and 700R4 have 27 splines..also most TH400's use larger U-joints with internal clips compared to the TH350/700R4 style that have outside clips on the caps..

I dont know if the NP241's have a 32 spline output to the rear shaft on the versions that went behind a 700R4 or not..

There are conversion u-joints available to join the 12 bolt pinion flange to the original 10 bolt driveshaft--some dont like them,because they supposedly are "weaker" and harder to find when you need one in a pinch...I haven't had any issues with the few I used though..I'd rather deal with an "odd" U-joint than risk screwing up the pinion preload by swapping the yokes myself..

If the axles are worn where the bearings rode,it might be better off to just buy new ones,especially if you plan to wheel it hard or carry heavy loads--Dorman now lists them,or you could source some good used ones maybe..
 
Thanks guys. I'll just stick to the bastard joint route. I've already got too much going on to make this a huge project on its own. I've read about the 1310/1330 joints, would that be the sizes I'd most likely need?
I can't believe I'm actually disappointed about finding a 12 bolt. I got so psyched when I counted the teeth I forgot to count the bolts. Back when I had my Buicks I'd have done backflips over finding a 12...now not so much....All I wanted was a bump up to 3.73s for a little more torque.:doah:

PS Coming off a 22 day work marathon isn't helping my brainpower either. Sorry if I'm asking some real newbie questions
 
I just read a post here on CK5 that says an NP241 rear output shaft is a 32 spline. The 203 that I bought the driveshaft to is said to be 32 spline also. Could it be this easy?
Stay tuned.......or just giggle at the idiot and scroll on..........

PS Thanks for the heads up on 'repair' bearings SweetK, I'd have bought them with a goofy smile on my face thinking I was being clever:eek1:
 
Last edited:
sweetk30 said:
203 is fixed yoke rear output .

208/241 are slip yoke output.
Click to expand...

I just came in from measuring and discovering that:waytogo: So looks like it's an easy choice...hope NAPA has a u joint in stock. Think I'll skip the bearings for now too, they didn't seem sloppy.

The cup that bolts into the yoke measured 1 1/8. That's the u joint I'm finding at NAPA for my 10 bolt. Before I go buy one I'm dropping my driveshaft and measuring mine just to be sure. Too damn many sizes:angry1:
 
Last edited:
Some others here have done the 10 bolt to 12 bolt swap and will likely know just what u-joint you'll need...(The one I used was a Neapco 3-3130,but that doesn't mean yours will end up being that one)..the "cross" was wider one way vs the other,and the two caps were larger diameter than the other two..

I know what you mean about the 12 bolt--my '85 Suburban has one in it,I do not know if its original or not (looks it,who knows?)...I hear the pinion is smaller shaft size on a 12 bolt truck diff vs a 10 bolt,so its not much "stronger" if at all...I never broke the ones I had in all my older 1/2 tons though..I stripped the splines out of a pinion yoke on my '72 K5 once when I was horsing around doing burnouts in 4 low,with the hubs unlocked...that was my punishment for "showing off"..:doah:
 
diesel4me said:
Some others here have done the 10 bolt to 12 bolt swap and will likely know just what u-joint you'll need...(The one I used was a Neapco 3-3130,but that doesn't mean yours will end up being that one)..the "cross" was wider one way vs the other,and the two caps were larger diameter than the other two..
Click to expand...

That's what I assumed but I thought the 12 bolt cups would be bigger than the 10.
 
Thanks guys:waytogo: It took me all day to wake up enough to put all the advice and info together and just order the damn thing from Summit. Skipping the bearings,giving it fresh oil and slapping it under the new plates/shackles. Just happy the only change in plans is a conversion joint:whistle: with me it could have gone much worse!
 
You must log in or register to reply here.

Latest Posts

Top Bottom