Chevy 12-bolt identification

[GotGrunt]

I recently picked up a 12-bolt rear and I’m having a hard time decoding the axle tube stamp. The casting number is 3959038 which is a (late) 1969 Chevy 12-bolt. The axle tube is stamped LE 0114K which to me looks like it may be for a 1970 GTO 455 but the LE code doesn’t exist for the 69-70 12-bolt, both for Chevy or Pontiac. Thoughts?

[bbbentley]

Buick? '70 GTO open 2.73 A body McKinnon (Canadian) built 12 bolt

[GotGrunt]

Originally Posted by bbbentley

Buick A body McKinnon (Canadian) built 12 bolt

Yes, the K is for McKinnon (GM of Canada) which is what led me to believe it was a GTO 455 rear since they came with Chevy 12-bolts in 1970. I’ve never seen a factory Chevy 12-bolt in a Buick though.

[John Brown]

I'm not a Buick expert but here's what Hemmings has to say about 12 bolt Chevy axles in Buick Stage cars in 1970.

https://www.hemmings.com/magazine/1970-Buick-GS-455-Stage-1

What to watch for: GS 455 Stage 1s were automatically equipped with reinforced upper control arms that were not available on the base GS 455. Furthermore, Canadian-built GS 455 and GS 455 Stage 1 cars were furnished with Chevy's 12-bolt differential; however, it featured Buick casting numbers rather than Chevrolet's. A Space-Saver spare became available for the first time.

[Baron Von Zeppelin]

70 Grand Prix 455 also used 12bolt rears.

Is it for sure a 2.73 ratio as Bentley mentioned ?

[GotGrunt]

Originally Posted by John Brown

I'm not a Buick expert but here's what Hemmings has to say about 12 bolt Chevy axles in Buick Stage cars in 1970.

https://www.hemmings.com/magazine/1970-Buick-GS-455-Stage-1

What to watch for: GS 455 Stage 1s were automatically equipped with reinforced upper control arms that were not available on the base GS 455. Furthermore, Canadian-built GS 455 and GS 455 Stage 1 cars were furnished with Chevy's 12-bolt differential; however, it featured Buick casting numbers rather than Chevrolet's. A Space-Saver spare became available for the first time.

Interesting, I did not know that. Do any documented examples exist? What is the Buick casting number for the Chevy 12-bolt?

Originally Posted by Baron Von Zeppelin

70 Grand Prix 455 also used 12bolt rears.

Is it for sure a 2.73 ratio as Bentley mentioned ?

It very well may be out of a Grand Prix 455. From what I’ve read, the GTO/GP 455 12-bolt ratios were limited to 3.07, 3.31, & 3.55. The LE code (2.73) listed for the GTO/GP is for the 10-bolt. That is where the confusion is. It is for sure a Chevy 12-bolt and it is definitely stamped LE.

[Baron Von Zeppelin]

If it turns out to actually be 2.73 , then GP
there is a listing for it as 12bolt 2.73 non-posi = LE
12bolt 2.73 Posi = LS

10bolt ratio is 2.78

If it turns out to actually be 3.31 , then Buick A-body

LE is basically an "and/or" mystery code according to some Google searches.
Did find a few instances of folks trying to decipher ones they had acquired as loose pieces - and the above info is best data found.

in case you haven't tried the "turn test" on a non-posi ,
one revolution with lug stud - count pinion turns - then double that number.
1 and 5/8 approx = 3.31
1 and 1/2 approx = 3.07
1 and 3/8 approx = 2.73
etc ...

[bbbentley]

I had a 69 Buick Special, plain Jane 6 cyl. Made in Canada. It had a 12 bolt Chevy rear. The ONLY difference I could find between this Canadian rear and a Chevelle was the Chevelle casting is 3959038NF, the Canadian did not have NF at the end

[GotGrunt]

Originally Posted by Baron Von Zeppelin

If it turns out to actually be 2.73 , then GP
there is a listing for it as 12bolt 2.73 non-posi = LE
12bolt 2.73 Posi = LS

10bolt ratio is 2.78

If it turns out to actually be 3.31 , then Buick A-body

LE is basically an "and/or" mystery code according to some Google searches.
Did find a few instances of folks trying to decipher ones they had acquired as loose pieces - and the above info is best data found.

in case you haven't tried the "turn test" on a non-posi ,
one revolution with lug stud - count pinion turns - then double that number.
1 and 5/8 approx = 3.31
1 and 1/2 approx = 3.07
1 and 3/8 approx = 2.73
etc ...

It’s in an old race car Chevelle so the guts have definitely been changed. I will know what’s in there once I get it out and crack it open.

Originally Posted by bbbentley

I had a 69 Buick Special, plain Jane 6 cyl. Made in Canada. It had a 12 bolt Chevy rear. The ONLY difference I could find between this Canadian rear and a Chevelle was the Chevelle casting is 3959038NF, the Canadian did not have NF at the end

It’s funny you mention that because this casting doesn’t seem to have the N or NF at the end either. I will double check that though once I get it out of the car and thoroughly clean off the housing. I wonder if all the McKinnon/Canadian Chevy 12-bolts were this way.