12 bolt question?

[62jimmy]

Hello,

Would a posi unit from a later truck (73-87) 12 bolt fit in an earlier 60's 12 bolt? Are the axle spline counts the same?

Thanks for your input!

[frankslagoon]

I think the're all the same but the axle splines were 17 spline up to 64 then fine spline after that

[Captainfab]

The truck 12 bolt was used from '63-'82. The '63 and '64 12 bolts had 17 spline axles. The '65-'82's had 30 spline axles. The truck 12 bolt carriers all interchange in the truck 12 bolt housings. You just have to use the correct axles for the spline count in the spider gears in the carrier.

[62jimmy]

Thanks for the info guys! I though the spline count changed at some point. I've got a line on a 60's 12 bolt to fit my truck, but wanted the interchange info before I made a deal, thanks again!

[vince1]

I don't know if it fits in your equation at all but in 1970 they went 1 1/2" wider and in 1971 they went to 5 stud axles.

[62jimmy]

Originally Posted by vince1

I don't know if it fits in your equation at all but in 1970 they went 1 1/2" wider and in 1971 they went to 5 stud axles.

I was aware of this, but thanks for bringing it up. I wanted the narrower early 12 bolt for my truck, but am not sure yet if it is a posi, if not I wanted to make sure I didn't have to have to find an early posi unit to fit it.

Thanks again guys for sharing your knowledge!
Jeremy

[Captainfab]

It was mid year of the 1970 model year that the width increased from 62" to 63.5".

Originally Posted by vince1

I don't know if it fits in your equation at all but in 1970 they went 1 1/2" wider and in 1971 they went to 5 stud axles.

[jaredyocum]

Any info about pinion splines ? I just bought a new ring and pinion and it looks like I will need a different Yoke as its much finer. Hope it works other than that !

[62jimmy]

Originally Posted by jaredyocum

Any info about pinion splines ? I just bought a new ring and pinion and it looks like I will need a different Yoke as its much finer. Hope it works other than that !

Interesting, I would have guessed they were all the same, hopefully someone will chime in, I just picked up a 12 bolt I'm gonna build so I'd like to know if there are differences, thanks for posting

[Captainfab]

The '63 & '64 12 bolt pinions and corresponding yokes had a coarse spline just as the axles did.

Originally Posted by jaredyocum

Any info about pinion splines ? I just bought a new ring and pinion and it looks like I will need a different Yoke as its much finer. Hope it works other than that !

[jaredyocum]

So I can just replace the yoke only with a 65-80ish model and all should be fine ?

[62jimmy]

Originally Posted by Captainfab

The '63 & '64 12 bolt pinions and corresponding yokes had a coarse spline just as the axles did.

ahh that makes sense. You are quite the wealth of knowledge captain, I think you have answered just about every question I have put up on this forum,

Thanks again