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Post Info TOPIC: 12 bolt - factory installed?


Poncho Master!

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12 bolt - factory installed?


I've come across several 65 & 66 Parisiennes over the years with what appears to be factory installed 12 bolts rear ends.

 Was this a "big block" thing or could a 327 car have come with one?

 Have seen a couple of 66/67  396 Grand Parisiennes with 12 bolts,as well

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A Poncho Legend!

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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

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I have come across several 65-70 6 cyl sedans with 12 bolts, and several V8 wagons with 10 bolts. Go figure.

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



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I was pleasantly surprised when I looked under the 67 GP.
I'd really expected to see a 10 bolt, but somthing told me the fact it was a 4bbl 327 paired with a TH400 in a big B ...it could have a 12.

Understandably it's probably not posi, but what ratio would one expect the big GP to have in the 12 bolt?



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 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

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cdnpont wrote:

I was pleasantly surprised when I looked under the 67 GP.
I'd really expected to see a 10 bolt, but somthing told me the fact it was a 4bbl 327 paired with a TH400 in a big B ...it could have a 12.

Understandably it's probably not posi, but what ratio would one expect the big GP to have in the 12 bolt?



It will be either a 2.73 or 3.07 but if I had to guess, I'd say 2.73 which started in 67. Until then, 3.08 was the tallest gear in the B body 12 bolts.

 



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my 66 has a 2.73 12 bolt    car was powerglide 6

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My 65 Camino is a 12 bolt. Originally a 327 car. Looked at other 283 models that had 10bolts.

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Poncho Master!

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   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.

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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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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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Of course, that would not explain the three wagons I scrapped that had 10 bolts (one a posi). Confusing ...

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gparis7 wrote:

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.



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


 



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Carl Stevenson wrote:

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.




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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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.

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62 Catalina 2 dr post project

69 Parisienne 2 dr ht 427

55 Bel Air 2 dr post 265PP/PG

66 Caprice 2 dr ht 396

68 Impala SS427 convt project

68 Caprice 2 dr ht 396

68 Bel Air 2 dr post BB project

69 Kingswood Wagon 396

11 C63 AMG Mercedes sedan

 



Poncho Master!

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My 65 Beaumont SD 4 spd is a factory 12 bolt with a 283 so there goes the 327 and up idea. My 65 Camino 4spd is a 10 bolt. Kind of weird.

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cdnpont wrote:

Carl Stevenson wrote:

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.




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.

 



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

 



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62 Catalina 2 dr post project

69 Parisienne 2 dr ht 427

55 Bel Air 2 dr post 265PP/PG

66 Caprice 2 dr ht 396

68 Impala SS427 convt project

68 Caprice 2 dr ht 396

68 Bel Air 2 dr post BB project

69 Kingswood Wagon 396

11 C63 AMG Mercedes sedan

 



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it appears (to mewink)....

certain gear ratios (lower) got you a 12 bolt
big block and higher horse sm/blks got a 12 bolt
F40/41 got a 12 bolt

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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

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A Poncho Legend!

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I would disagree with the 396 cars ever having a 10 bolt except after they switched to the newer style diff, post 1970. If a 70 or older had a 10 bolt, I would say it had been changed.

I never say never (!) but a big block Canadian Poncho never came from the factory with a TH350 or a 10 bolt. Always a powerglide, TH400 or manual trans, always a 12 bolt.

And now with that said, someone will catch something I have worded poorly and prove me wrong!

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

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Not sure if you can see but for 69 Beaumont says 12 bolt rear end for 350 V8's with manual trans, all 396 V8's and with option F40       (8.875 ring gear.)




img168.jpg

-- Edited by Beaumont4008 on Friday 18th of September 2009 10:16:07 PM

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This should be better.



img168.jpg

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A Poncho Legend!

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Seems to be no rhyme or reason though. There is a 69 Chevelle hardtop here in town. It was stone stock when he bought it, 350, TH350 and a 12 bolt.

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