#1  
Old 06-06-2021, 07:52 PM
GMCM76 GMCM76 is offline
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Default Grand prix sj help

I am looking at a 69 GP SJ. Should the car have come with a 12 bolt rear end? It has the original 428 but only a 10 bolt rear end. Thanks for the help in advance

  #2  
Old 06-06-2021, 09:11 PM
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It should have a 10 bolt, no 12 bolt until 1970.

Grant

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Old 06-06-2021, 09:25 PM
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Juust a thought but the 69 GPs had 14" wheels, the 70 had 15"s. Wonder if that's why '70s got 12 bolts.

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Old 06-06-2021, 09:40 PM
poncho-mike poncho-mike is offline
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I don't think the 70 GPs had 15" wheels as an option. I've never seen JWs on a 1970.

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Old 06-06-2021, 09:41 PM
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No... The optional 15" wheel became available in mid-year 1972 along with radial tires, no 15" wheels were installed on GP's prior to that.

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Old 06-06-2021, 11:12 PM
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All 70 grqnd prixs had 14x7 wheels and only the 455 cars recieved the 12 bolt rear.

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Old 06-07-2021, 12:33 AM
Joe's Garage Joe's Garage is offline
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Default All the 1969-72 GPs we've seen with Rally II wheels were 14x7s.

Historically the 15x7 Rally IIs were available late in 1972, but we've never actually seen any with 15x7s.

Maybe the four we had were all early-model-year builds (?). I don't think I even kept the VINs on those and, unfortunately, we sold our last 1972 GP a dozen years ago to concentrate on 1969s.

Two of the 1972s were 455s and both had factory 3.08 non-posi 12-bolts.

We've had two 1970 GP SJs with 455s and both of those had 12-bolt limited slip rear-ends.

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Old 06-07-2021, 02:58 PM
poncho-mike poncho-mike is offline
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I parted a bunch of 70 SJs for the 455 4-bolt block and 12-bolt rears. I've found it to be about 50/50 when it comes to posi vs non-posi rears. I have found 3.31 12-bolt posi rears, 3.07 posis, and 3.07 open rears in 1970 - 1972 GPs.

I've parted a bunch of 71 & 72 SJs for the 455 engines, and I have never seen one with KR, KN, or JW wheels.

Mike

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Old 06-07-2021, 04:37 PM
Joe's Garage Joe's Garage is offline
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Default Typo in my response above - they were 3.07 12-bolt rear-ends......

My mind was stuck in the 10-bolt Pontiac HD world, where 3.08s are found........

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Old 06-07-2021, 05:03 PM
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Looks like my memory was faulty about the 70 GP. Bought about 1977 anyway. Was 14x7 Rallye IIs and not 15s, FSM says 15x7 Rally II were optional in 71. Think 3.08 12 bolt was standard and 3.31 with AC. In '70 I had a Buick GS with 15x7 wheels bought on return from SEA. Just have one picture from then but no Pontiacs.

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Last edited by padgett; 06-07-2021 at 05:24 PM.
  #11  
Old 06-12-2021, 10:33 AM
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The actual link between SJ’s and safe-t-track was that all early production 1969 428 GP’s (including all SJ’s therefore) had mandatory STT. There is an early January 69 memo announcing that STT was no longer mandatory with a 428. I suspect that the issue was that they were worried about the strength of the 2 pinion differential with 428’s and the only 4 pinion 10 bolt differential pontiac had in 69 was the STT version. Did they allow non STT in January because they released a 4 pinion open differential or did testing satisfy them that the 2 pinion would be sufficient after all on open diff applications?

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