Identification of my 12 Bolt

[Big70]

Can you guys tell me what you know about these identification numbers? Really would love to know what axles are in here and what year this was built. From what I can see the the tube has HC 06 23 stamped and the housing has 147 cast into it. Thanks in advance!

[gmc684x4]

HC 06 23 3.73 Posi gears 6 month 23 day 67 rear diff

http://67-72chevytrucks.com/vboard/s...d.php?t=486309

https://gmcpauls.com/67-72_chevy.htm

[Big70]

Originally Posted by gmc684x4

HC 06 23 3.73 Posi gears 6 month 23 day 67 rear diff

http://67-72chevytrucks.com/vboard/s...d.php?t=486309

https://gmcpauls.com/67-72_chevy.htm

Do you happen to know what spline axels are in it? My dad said he heard of some thing about smooth spline? Never heard of it.

[gmc684x4]

70 to 82 are 30 spline
I am guessing 67 to 69 are as well

67 to 82 12 bolts take the same axle seals and bearings
On the earlier 63 66 ones i am not sure

I never counted splines last time i changed axle seals on my 68

63 to 66 are a course spline from my understanding

On earler open diffs easy as changing spider gears to a 30 spline from what i have read

Are you looking to switch to 5 bolt axles ?

[Big70]

Originally Posted by gmc684x4

70 to 82 are 30 spline
I am guessing 67 to 69 are as well

67 to 82 12 bolts take the same axle seals and bearings
On the earlier 63 66 ones i am not sure

I never counted splines last time i changed axle seals on my 68

63 to 66 are a course spline from my understanding

On earler open diffs easy as changing spider gears to a 30 spline from what i have read

Are you looking to switch to 5 bolt axles ?

No sir. Just trying to make sure that I buy all the right bearings and seals. How could you tell that it’s built in 67? I have a 12 Bolt in there right now that I hurt. I just acquired this 12 bolt with 373 gears that I want to put in there with all fresh seals and bearings.

[gmc684x4]

Google I found a table excerpt from the new SA design book 67 72 chevy trucks
Has a table listing Diff stamp codes listed HC states 3.73 posi 1967

Gmc Pauls also hase code Hc listed as 3.73 posi no year listed

If you choose look inside on there site page 103 I see they List it in 1969 so that code will be for 67 to 69

https://www.cartechbooks.com/how-to-...1967-1972.html

[Big70]

One thing I’m trying to figure out is why the 12 bolt I have under the truck is 57 inches backing plate to backing plate but the 12 bolt I just got is around 55 1/2? The truck was a step side before and from the looks of things the narrower 12 bolt is going to go in just fine. Did they make a wider 12 bolt for step sides or some thing? Every thing seams like it’s going to line right up it’s just narrower.

[gmc684x4]

What is the axle number of the diff in your truck ?
I would guess and say its a 70 to 72 diff there a bit wider

[Big70]

Originally Posted by gmc684x4

What is the axle number of the diff in your truck ?
I would guess and say its a 70 to 72 diff there a bit wider

The axel number? Is that part of the #’s that ar stamped into the tube or number that is cast into the center section?

[gmc684x4]

Be the stamped numbers like your new dif on the axle tube

[LockDoc]

-
Here are the ratio charts I posted on the board back in 2013.

http://67-72chevytrucks.com/vboard/s...d.php?t=578793

LockDoc

[Mike C]

1970 was a changeover year. It should have the wider housing same as 71-72. The 67-69 trucks had the narrower housing.