12 bolt posi chevy or olds????
March 10th, 2009, 06:27 PM
#1
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12 bolt posi chevy or olds????
I have a 12 bolt posi with a 12 bolt ring in my car. the tube id no. is CF 06 17 B with an E directly under the 0. these are all stamped numbers. The dif casting no. is NF 3894939. The axle is a 4.10 ratio presently. Can anybody help with the identification? The car is a 1972 olds cutlass supreme. I do not believe this is the original axle that came with the car. any help will be appreciated. Also will this fit into a 1970 Grand Prix?
Thanks
Tim72
Thanks
Tim72
March 11th, 2009, 01:04 PM
#2
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March 11th, 2009, 01:33 PM
#3
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Hey Tim, from what I have been told, is if your diferential cover plate is a solid circle then it is a chevy rear end. If the plate to two notches cut out at the 3 and 9 o'clock positions then it is out of an oldsmobile or pontiac.
March 11th, 2009, 02:14 PM
#4
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Go to Jim's website.
http://jdrace.com/
http://jdrace.com/
March 11th, 2009, 04:49 PM
#5
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A type "O" Olds 12 bolt has a plain 12 bolt cover. A type "C" Chevy 12 bolt has 2 protrusions on the upper area of the cover to improve oil circulation within the housing. Olds has an 8.55' ring gear the Chevy is slightly bigger at 8.875.
March 11th, 2009, 05:50 PM
#6
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12 bolt and Posi (Positraction) would make it a Chev.
Olds used 10 bolts, and was called Anti-Spin.
I don't know that Olds/Pontiac ever manufactured a 12 bolt.
Norm
Olds used 10 bolts, and was called Anti-Spin.
I don't know that Olds/Pontiac ever manufactured a 12 bolt.
Norm
Last edited by 88 coupe; March 11th, 2009 at 05:52 PM.
March 12th, 2009, 01:03 AM
#7
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Olds used 10 bolts, and was called Anti-Spin.
I don't know that Olds/Pontiac ever manufactured a 12 bolt.
Norm[/quote]
Olds had a 10 and a 12 bolt. Pontiac has a peanut shaped 10 bolt cover.
All the divisions had a different name for their respective limited slip options.
March 12th, 2009, 04:54 AM
#8
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[/quote]
Olds had a 10 and a 12 bolt. Pontiac has a peanut shaped 10 bolt cover.
All the divisions had a different name for their respective limited slip options.[/QUOTE]
What 12 bolt are you referring to? The "O" rear is a 10 bolt gear with a 12 bolt cover. Norm is questioning if Olds/Pontiac ever made a 12 bolt gear.
Olds didn't that I know of.
Interesting, the '71 up GM corporate rear was 12 bolt gears and 10 bolt covers.
Olds had a 10 and a 12 bolt. Pontiac has a peanut shaped 10 bolt cover.
All the divisions had a different name for their respective limited slip options.[/QUOTE]
What 12 bolt are you referring to? The "O" rear is a 10 bolt gear with a 12 bolt cover. Norm is questioning if Olds/Pontiac ever made a 12 bolt gear.
Olds didn't that I know of.
Interesting, the '71 up GM corporate rear was 12 bolt gears and 10 bolt covers.
March 12th, 2009, 07:36 AM
#9
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Olds had a 10 and a 12 bolt. Pontiac has a peanut shaped 10 bolt cover.
All the divisions had a different name for their respective limited slip options.[/quote]
What 12 bolt are you referring to? The "O" rear is a 10 bolt gear with a 12 bolt cover. Norm is questioning if Olds/Pontiac ever made a 12 bolt gear.
Olds didn't that I know of.
Interesting, the '71 up GM corporate rear was 12 bolt gears and 10 bolt covers.[/quote]
Correct. Contrary to popular belief, the terms "10 bolt" and "12 bolt" refer to the number of bolts on the RING GEAR, not the cover. Chevy rear axles just happen to use the same number of bolts on the cover and on the ring gear, and since the world is Chevy-centric, that has become common (though incorrect) usage.
The Olds "Type O" alleged 12 bolt axle only has 10 bolts holding an 8.5" ring gear.
Now, as Kurt correctly points out, there were Pontiac axles used under the full size cars that did have 12 bolt ring gears and 10 bolt covers. I believe these are the 9.30" ring gear axles?
All the divisions had a different name for their respective limited slip options.[/quote]
What 12 bolt are you referring to? The "O" rear is a 10 bolt gear with a 12 bolt cover. Norm is questioning if Olds/Pontiac ever made a 12 bolt gear.
Olds didn't that I know of.
Interesting, the '71 up GM corporate rear was 12 bolt gears and 10 bolt covers.[/quote]
Correct. Contrary to popular belief, the terms "10 bolt" and "12 bolt" refer to the number of bolts on the RING GEAR, not the cover. Chevy rear axles just happen to use the same number of bolts on the cover and on the ring gear, and since the world is Chevy-centric, that has become common (though incorrect) usage.
The Olds "Type O" alleged 12 bolt axle only has 10 bolts holding an 8.5" ring gear.
Now, as Kurt correctly points out, there were Pontiac axles used under the full size cars that did have 12 bolt ring gears and 10 bolt covers. I believe these are the 9.30" ring gear axles?
March 12th, 2009, 08:00 AM
#10
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March 12th, 2009, 11:39 AM
#13
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How's that work for you when you need a ring gear? The fact remains that when people talk about "10 bolt" and "12 bolt" axles they are 1) referring to Chevy axles and 2) the assumption is that the 12 bolt is stronger than the 10 bolt. This is NOT the case with non-Chevy axles. That's why simply saying 10-bolt or 12-bolt is not sufficient.
March 12th, 2009, 01:13 PM
#14
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I know, thats where the confusion seems to start. I think were beating a dead horse.
The bottom line... You need to know what rear end you got before ordering parts. It's as simple as that. Like always, do your homework, post a thread if you need to and you'll be fine. Thats what I do. 
The bottom line... You need to know what rear end you got before ordering parts. It's as simple as that. Like always, do your homework, post a thread if you need to and you'll be fine. Thats what I do.
March 12th, 2009, 02:05 PM
#15
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Well thanks for all your help. The numbers I gave off the axle tube does not tell anybody what type of rear end I have or what year and type of car it came out of ? Where can I go to look up this ionformation?
Thanks
tim72
Thanks
tim72
March 12th, 2009, 03:28 PM
#17
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It was a 1966 chevelle 12 bolt 331 posi
built June 17th of 66 in Buffalo NY.
Last edited by MN71W30; March 12th, 2009 at 03:35 PM.
March 12th, 2009, 10:05 PM
#19
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12 bolt rear
NF 3894939
was used most commonly as a 1967 -1969 casting 12 bolt chevy c-clip rear diff.
In the webbing you should have a letter number date code also. example B 25 7
this breaks down to : B=month of feb. 25 25th day of feb. 7 1967 year.
Hope this helps some. Jim
Some info on the rear was correct...I do not know how you got a year from the axle tube? The year is cast into the center section. The axle tube only gives the month and day and the plant and if it was posi and the ratio (2-3 letter code) NOT the year.
SO... we need the cast in suffix code to find the year. The 1966 12 bolt rear will have flat perches with bolt on springs. Does this rear have flat perches or pop up dome spring perches? Jim
was used most commonly as a 1967 -1969 casting 12 bolt chevy c-clip rear diff.
In the webbing you should have a letter number date code also. example B 25 7
this breaks down to : B=month of feb. 25 25th day of feb. 7 1967 year.
Hope this helps some. Jim
Some info on the rear was correct...I do not know how you got a year from the axle tube? The year is cast into the center section. The axle tube only gives the month and day and the plant and if it was posi and the ratio (2-3 letter code) NOT the year.
SO... we need the cast in suffix code to find the year. The 1966 12 bolt rear will have flat perches with bolt on springs. Does this rear have flat perches or pop up dome spring perches? Jim
March 13th, 2009, 05:59 AM
#20
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NF 3894939
was used most commonly as a 1967 -1969 casting 12 bolt chevy c-clip rear diff.
In the webbing you should have a letter number date code also. example B 25 7
this breaks down to : B=month of feb. 25 25th day of feb. 7 1967 year.
Hope this helps some. Jim
Some info on the rear was correct...I do not know how you got a year from the axle tube? The year is cast into the center section. The axle tube only gives the month and day and the plant and if it was posi and the ratio (2-3 letter code) NOT the year.
SO... we need the cast in suffix code to find the year. The 1966 12 bolt rear will have flat perches with bolt on springs. Does this rear have flat perches or pop up dome spring perches? Jim
was used most commonly as a 1967 -1969 casting 12 bolt chevy c-clip rear diff.
In the webbing you should have a letter number date code also. example B 25 7
this breaks down to : B=month of feb. 25 25th day of feb. 7 1967 year.
Hope this helps some. Jim
Some info on the rear was correct...I do not know how you got a year from the axle tube? The year is cast into the center section. The axle tube only gives the month and day and the plant and if it was posi and the ratio (2-3 letter code) NOT the year.
SO... we need the cast in suffix code to find the year. The 1966 12 bolt rear will have flat perches with bolt on springs. Does this rear have flat perches or pop up dome spring perches? Jim
I didn't realize 66-67 shared the CF code and figured I found the smoking gun when I looked at the 66 chart.
March 13th, 2009, 08:37 AM
#21
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here i hope this helps pic out of my 68 repair manual the top is a chevy 12 and the lower is a olds.diff covers.jpg
12 bolt
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