Mark's '67 327 Grand Parisienne has a 12 bolt. Perhaps it was optional on the small block cars?

-- Edited by 69Laurentian on Friday 18th of September 2009 05:17:55 AM

Yes, my uncle had a 65 Laurentian 6 cyl, 3 on the tree, 12 bolt.

 As far as I am concerned, I would guess which ever box was ticked when they were ordered. The majority of my cars have been 12 bolts from 6cyl cars to big blocks. I had wondered when I joined the site why a lot of you guys seemed excited when a 12 bolt was found. Here in Sask, most are 12 bolt, a common thing!
 While I was in Labrador, I removed a 12 bolt 3:08 posi from a '69 Laurentian 4-dr sedan 6cyl for my '70 Parisienne which had a 6cyl THM350 and a 12 bolt! The only 10 bolts I have seen are in my Grande 4-dr h/t that had a 327 and a glide now a 3:31 12 bolt, one of my '70 h/top 2+2's with a 350 and THM400 has a 10 bolt posi and my recent '70 Parisienne 4dr sedan with a 350 and a THM350 trans.
 My '66 Strato with 6cyl, 3 on the tree as well as a '65 Biscayne with the same combo both have 3:31 12bolts.... I don't think there is a rhyme or reason to this from what I have seen...............!



-- Edited by 67Poncho on Friday 18th of September 2009 02:11:45 PM

my 66 has a 2.73 12 bolt    car was powerglide 6

   Alot of Oshawa built GM cars came with it, my 1972 Pontiac Lemans 400 came with the factory installed 12 bolt, in the US only Pontiac 455 Lemans-GTO cars had it installed.

Hmm, you might have something there. I know our family always ordered F40 cause we lived down some bad roads. Might explain my uncle's 6 cyl 12 bolt car.

gparis7 wrote:

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I wonder if it might have something to do with the selection of the F40 HD suspension option. Without exception the 6 cyl & small V8 cars I've seen with 12 bolts also had a 15/16ths front sway bar, which was standard with the F40 option.

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i have a '69 impala with a 12 bolt and F40.
rear diff. code comes up '3.07 HD suspension'

 

I parted a 69 Impala 4 dr ht that had F40, and a 12 bolt posi with 3.36 gears. It was a 327 2 bbl powerglide car.

cdnpont wrote:

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Carl Stevenson wrote:

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Hmm, you might have something there. I know our family always ordered F40 cause we lived down some bad roads. Might explain my uncle's 6 cyl 12 bolt car.

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The F40 theory is a good start, but beond that, it seems in a high output car the rule was a 12 bolt, did 427 CP ever have a 10 bolt?. I've heard of 396 with a 10. The light duty stuff seemed get whatever the factory had a bigger stock of at the time (with the suitable ratio). Seems in a peg leg in most part were 2.73's or 3.07/8's and the lower output cars could use these common ratios with only a speedo drive change. If they had 10 bolts with one upper arm flange, then the light duty cars got one arm (which is rare in a CP). If the supply had 10 bolts with two uppers then two they got. No 10's available, we've got 12's so use the tall geared 12's in everything but ordered and high output cars that needed posi and a lower gear.

I think it really amounted to some flexible supply and manufacturing on GM's part.

 

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Could be. No less plausible than the F40 idea, or box checking. Would be good to know what the criteria are though.

 

i always wondered why my 69 Beaumont with a 307 powerglide had a 12 bolt ,im the 3rd owner ,1st was a old lady ,seccond was my aunt ,who never changed anything,even the oil!

but it does have F40 suspension

-- Edited by 68sd on Friday 18th of September 2009 09:34:00 PM

i agree carl, i've never seen a '65-'70 big block car with a 10 bolt rear....

This should be better.