69 Caprice 12 bolt decode - Impala Tech
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post #1 of 3 (permalink) Old 05-27-2010, 06:35 PM Thread Starter
Join Date: May 2010
Location: Indiana
Posts: 17
69 Caprice 12 bolt decode

Hi There,

Just picked up a 69 Caprice with a 427 Th400 and a 12 bolt. I was hoping to get some help here decoding my differential. These are the numbers I have uncovered.

Axle tube is stamped with what looks like: FW 0328 G2 however the first letter, the F, has taken a hit or was miss stamped at the factory and is hard to read it may be some other letter but the W 0328 G2 is definate.

The center section has a few casting codes as follows:
C219 whick I think is a build date. And right above this is the number 56?

Then there is 12345 and then below that is 67890 no idea here.

Thanks Very much for any help.

TJA is offline  
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post #2 of 3 (permalink) Old 05-27-2010, 10:27 PM
Join Date: Jan 2006
Posts: 12,458
Your numbers FW 0328 G2 decode as
FW indicates a 2.56 gear set.
03 is the month in 1969 it was built, and 28 is the day of the month.
G is the factory that built your rear end, in this case Detroit Gear, and it was built during the second shift (between 4:00 PM and mid night).
You have no code letter for a Posi-Traction so odds are the factory didn’t install one.

The 12 bolt had three different carriers (the casting numbers are on the carrier inside the differential not on the outside case) to account for the change in the rings position due to the root diameter of the pinion gear shrinking as the gear ratios increased (the Ford nine inch differential moves the ring gear back and forth in the case by way of two spanner nuts so it has only one size carrier). The 12 bolt two series carrier (casting number ED 32088) supports gear ratios of only 2.56 and 2.73. The 12 bolt three series carrier (casting number 30140PM1) supports gears from 3.08:1 to 3.73:1 (4.11 in aftermarket). The 12 bolt four series carrier (casting number ED30174) supports gears from 3.90 up to 5.38 (3.73 and up to a 6.17 are available in the aftermarket to fit a 12 bolt four series carrier without a spacer plate).

Big Dave
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post #3 of 3 (permalink) Old 05-28-2010, 12:43 AM Thread Starter
Join Date: May 2010
Location: Indiana
Posts: 17
Thanks Big Dave for some good info.
TJA is offline  
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