12 Bolt GM ?

lareagle · 12-22-2010, 09:38 PM

Have a 12 bolt rear under a 1970 Nova. Can any one tell if is correct for that year? Number on housing are 3894860nf = 1234567890 =A149.
54 1/2 flange to flange. 38948gonf
Thanks
Larry

FED 387 · 12-22-2010, 10:27 PM

Larry-348690 is the casting number for a 12 bolt case but look on the top of the passenger side tube more towards the front of the car and there are a series of letters& numbers stamped in the tube---ya probably will hafta wire brush the tube clean to find those numbers---give me all of the numbers/letters and I can tell ya most of what ya want to know as far as WHAT IT WAS FROM THE FACTORY---now if the ratios have been changed or whatever cannot help ya there but what it was OEM yes--Comp

lareagle · 12-23-2010, 07:10 PM

The numbers on the tube is = 3894860nf
Thanks for your help.
Larry

cad · 12-23-2010, 07:12 PM

The numbers will be stamped in the front of the tube, not casting/raised numbers on the center section.
http://www.novaresource.org/axle.htm

lareagle · 12-23-2010, 07:14 PM

Number on tube is = BT0122G2 (E)
Thanks for your help.
Larry[/QUOTE]

FED 387 · 12-23-2010, 07:23 PM

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 · 12-24-2010, 07:20 PM

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

FED 387 · 12-25-2010, 12:57 AM

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 · 12-25-2010, 01:28 AM

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

paulbass · 01-23-2011, 01:28 PM

i have a 12 bolt rearend #3894860nf on the tube #bm0213g2 there are also a279 con1 what rearend do i have.

12-22-2010, 09:38 PM	#1
lareagle Member Join Date: Oct 2007 Posts: 288 Likes: 7 Liked 7 Times in 7 Posts	12 Bolt GM ? Have a 12 bolt rear under a 1970 Nova. Can any one tell if is correct for that year? Number on housing are 3894860nf = 1234567890 =A149. 54 1/2 flange to flange. 38948gonf Thanks Larry

12-22-2010, 10:27 PM	#2
FED 387 VIP Member Join Date: Jun 2006 Posts: 3,353 Likes: 331 Liked 280 Times in 150 Posts	Re: 12 Bolt GM ? Larry-348690 is the casting number for a 12 bolt case but look on the top of the passenger side tube more towards the front of the car and there are a series of letters& numbers stamped in the tube---ya probably will hafta wire brush the tube clean to find those numbers---give me all of the numbers/letters and I can tell ya most of what ya want to know as far as WHAT IT WAS FROM THE FACTORY---now if the ratios have been changed or whatever cannot help ya there but what it was OEM yes--Comp

12-23-2010, 07:12 PM	#4
cad Senior Member Join Date: Apr 2009 Location: Omaha, NE Posts: 673 Likes: 141 Liked 72 Times in 40 Posts	Re: 12 Bolt GM ? The numbers will be stamped in the front of the tube, not casting/raised numbers on the center section. http://www.novaresource.org/axle.htm

12-23-2010, 07:14 PM	#5
lareagle Member Join Date: Oct 2007 Posts: 288 Likes: 7 Liked 7 Times in 7 Posts	Re: 12 Bolt GM ? Number on tube is = BT0122G2 (E) Thanks for your help. Larry[/QUOTE]

12-23-2010, 07:23 PM	#6
FED 387 VIP Member Join Date: Jun 2006 Posts: 3,353 Likes: 331 Liked 280 Times in 150 Posts	Re: 12 Bolt GM ? 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

12-23-2010, 07:10 PM	#3
lareagle Member Join Date: Oct 2007 Posts: 288 Likes: 7 Liked 7 Times in 7 Posts	Re: 12 Bolt GM ? The numbers on the tube is = 3894860nf Thanks for your help. Larry

12-24-2010, 07:20 PM	#7
lareagle Member Join Date: Oct 2007 Posts: 288 Likes: 7 Liked 7 Times in 7 Posts	Re: 12 Bolt GM ? Doesn;t these numbers on the pass. side tube help ? BT 01 22 G2 E Thanks Larry

12-25-2010, 12:57 AM	#8
FED 387 VIP Member Join Date: Jun 2006 Posts: 3,353 Likes: 331 Liked 280 Times in 150 Posts	Re: 12 Bolt GM ? 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

12-25-2010, 01:28 AM	#9
FED 387 VIP Member Join Date: Jun 2006 Posts: 3,353 Likes: 331 Liked 280 Times in 150 Posts	Re: 12 Bolt GM ? 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

01-23-2011, 01:28 PM	#10
paulbass Junior Member Join Date: Jan 2011 Location: winona Posts: 5 Likes: 0 Liked 0 Times in 0 Posts	Re: 12 Bolt GM ? i have a 12 bolt rearend #3894860nf on the tube #bm0213g2 there are also a279 con1 what rearend do i have. Last edited by paulbass; 01-23-2011 at 01:57 PM. Reason: had to add #