12 Bolt GM ?

[FED 387]

larry there will be a code something like
2 letters --then
4 numbers--then
2 or 3 letters


This is just an example but it will look something like this
QY 01 01 GE

Give me that code and I can tell ya what it was ORIGINALLY

Also any other numbers cast into the cast iron housing look along the ridges that is usually where they put them---that 3894860 is a 12 bolt cast iron center but without the other codes ya quite cannot tell what the housing is/was GM had different widths from model to model as well as year to year

[lareagle]

Doesn;t these numbers on the pass. side tube help ? BT 01 22 G2
E
Thanks
Larry

[FED 387]

larry the code ya gave me is what was in that rear originally when installed in the car
BT---3:55 posi
01---January
22---22nd day of the month
G----Detroit Gear & Axle
2----Night shift
E----Eaton Positraction Differential

Housing dimensions are
Center to center of the spring perches----42 3/4 inches
Inside of backing plate to inside of backing plate---53 1/4 inches
Outside of brake drum to outside of brake drum---60 1/4 inches

[FED 387]

Larry--I forgot to mention that that code is for a 68 or 69 rear end however see what the date code cast into the ribs on the left side of cast iron differential are ---also what is the serial number of your car you might have a very early 70 model and they had left over 69 housings to use up when they built your car