12 Bolt axle identification and date code

[84Silverado4x4]

Can anyone help me figure out what the rear axle is originally out of or what any of this means.

So far I have found:
 GM72
 CON3
 3896839 N
 on the housing.

[blazer74]

Date code at top for casting.
A84. A Jan,  8th day of the year, 4 1974 in this case.

[blazer74]

Top of right axle tube.
Ratio, plant, day of year, shift and sometimes another digit for posi.

KAH W 010 1
KAH ratio, W Warren Michigan, 010 day of year,
1 shift.


https://www.crankshaftcoalition.com/wiki/Rearend_identification

Gmpartswiki.com is a buffet of info.

[84Silverado4x4]

Can anyone help me figure out what the rear axle is originally out of or what any of this means.

So far I have found:
 GM72
 CON3
 3896839 N
 on the housing.

Date code at top for casting.
A84. A Jan,  8th day of the year, 4 1974 in this case.

In the same spot as this one pictured I have a  (J204)  does that make sense?  would I also have something on the axle tube?  I don't see anything right off but I don't want to remove the paint if there isn't anything there

[blazer74]

J  10th month Oct, 20 day of the month, 4 year.
Year could be 1974, 1984.
I would assume Oct 20 1984 going by your info.

Numbers near the top of the right axle tube tell more of the story but don’t always give the year.
Gear ratio codes can change by the year also.

Of course you don’t always know the history of the axle. Ratio changes etc.

[blazer74]

[84Silverado4x4]

Thanks for the help!.. I have rebuilt the center with a 4.56 gears and a Detroit locker so I knew whats inside it but I think GM stopped offering the 12 Bolt  in either 1980 or 1981 so I was thinking it must be from an earlier truck.  I know my front axle is a dana 44 from a 73-76.  I'll have to look for that date code also.  I assume they probable were donors from the same truck.  I'm mostly trying to sort out what I have going on for brakes and try and improve them.

[blazer74]

Think 81 last year 12 bolt.