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Canadian Poncho Homepage -> Canadian Poncho -> 65-70 Full Size Power Train Tech Forum -> 12 bolt rear end ratio help
Post Info TOPIC: 12 bolt rear end ratio help
Bago


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12 bolt rear end ratio help
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Hello guys, just trying to work out my ratio for my rear end. With two full turns of the rear wheel, the prop shaft turns 3 and 1 third turns. Does this mean I have a 3.33 ratio? If so, I can find nothing online to suggest that a 12 bolt comes in that ratio? Please help!! Ian UK

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Bago


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Oh, incase anyone needs to know, vehicle is a 1967 Pontiac Parisienne 4 door pillarless.

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67Poncho


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If you are trying to find out the ratio with that procedure, generally, 1 rotation of the rear wheel and count the turns of the pinion... If we 1/2 this, I would say, roughly 3:07 ratio... Easier way is to look at the axle code jut left of the center pumpkin on the forward side of the passenger axle tube.... There will be a 2 digit code, "EM" for example, if it is an 8.875 3:07 ratio.... I will get pics for you....



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Vincent Jr.
Bago


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Brilliant, if you could that would be excellent, thanks!!

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seventy2plus2


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Yes, the axle code should be stamped on the passenger side axle tube, about 2-3 inches away from the cast iron center section.  The stamping should be facing forward, but sometimes a little more towards the top.  You might need to do a little cleaning with a wire brush, but it'll be there.  Once you find the code we can decode it.



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Bago


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Hi Guys,

Is this the code you need? Couldn't see one on the tube though?? Looks like GM3N to me!!

See pic here:

www.flickr.com/photos/35630959@N07/30902731416/in/dateposted-public/

Thanks for your help!

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seventy2plus2


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Nope, that's not it.  What you're seeing is some casting information on the center section.    

What you're looking for is stamped (with a punch) into the passenger side axle tube, a few inches from the center section.   We had to fly someone through this before, they found the stampings more towards the top, but they did find them.   The letters/numbers will be about 1/4" high.  There will be 7 or 8 letters/numbers, and which will include letters for the differential code, numbers for the date code, and a final letter for the plant that put the diff together.



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67Poncho


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Here you go... Have at it... The pic I posted is a 3-digit off of my '70 Estate... just a reference.

Estate Diff1.JPG

'67 Diff Codes.JPG

'67 Diff Codes1.JPG '67 Diff Codes2.JPG



-- Edited by 67Poncho on Saturday 12th of November 2016 01:42:59 PM

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Vincent Jr.
Bago


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Thank you very much for your help and time man! I will give the axel a good clean in the morning (it's night here in UK) and check it out!

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67Poncho


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Bago wrote:

Thank you very much for your help and time man! I will give the axel a good clean in the morning (it's night here in UK) and check it out!

Your welcome.... Post a pic or 2 when you get time... It is 13:00hr here at the present moment.... A great day, actually... +10C and sunny....  



-- Edited by 67Poncho on Saturday 12th of November 2016 02:00:31 PM

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Vincent Jr.
davelacourse


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I bought a 1966 Chevelle SS396 new, came from factory with 3.36 12-bolt rear so seems likely that is what yours is.

Dave

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56Pontiac  1956 Pontiac Pathfinder 2dr sedan, 496 - dyno'd 545 hp, stick shift, 4.11 posi - Hot Rod

  1964 Acadian Beaumont SD convert, 283 - factory 195 hp, Powerglide, 3.08 10-bolt - Cruiser

  2012 US-built crew cab truck - Daily Driver and Boat Trailering
4SPEED427


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Hi Bago. A 67 Parisienne 12 bolt would have come with 2.73, 3.07, 3.31, 3.55 or 3.73 as far as I know. In your case it sounds like it must be 3.31.

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1966 Strato Chief 2 door, 427 4 speed, 45,000 original miles 

1966 Grande Parisienne, 396 1 of 23 factory air cars (now converted to a "factory" 4 speed)
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67Poncho


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Had to move my '67 Strato so I decided to bring it in the shop to give you a real time example... This is a 250ci, 3-on-the-tree car... (I forgot what axle was in this one)

'67 Strato Chief.JPG

'67 Strato Chief Axle Code.JPG



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Vincent Jr.
67Poncho


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Carl Stevenson wrote:

Hi Bago. A 67 Parisienne 12 bolt would have come with 2.73, 3.07, 3.31, 3.55 or 3.73 as far as I know. In your case it sounds like it must be 3.31.

YOU '66 guys.... think you know everything! (lol) An automatic car, I suspect... That's why I say 3:07-ish....

What's in yours?



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4SPEED427


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Well, 3 and 1/3 turns seems pretty close to 3.31 according to what my math teacher taught me...

Unless your math teacher taught you that 3.07 is closer to 3 1/3 than 3.31!!!

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1966 Strato Chief 2 door, 427 4 speed, 45,000 original miles 

1966 Grande Parisienne, 396 1 of 23 factory air cars (now converted to a "factory" 4 speed)
davelacourse


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Carl Stevenson wrote:

Well, 3 and 1/3 turns seems pretty close to 3.31 according to what my math teacher taught me...


... as is 3.36, eh?  biggrin

Dave



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56Pontiac  1956 Pontiac Pathfinder 2dr sedan, 496 - dyno'd 545 hp, stick shift, 4.11 posi - Hot Rod

  1964 Acadian Beaumont SD convert, 283 - factory 195 hp, Powerglide, 3.08 10-bolt - Cruiser

  2012 US-built crew cab truck - Daily Driver and Boat Trailering
4SPEED427


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Agreed, but 3.36 was not available in any Canadian Pontiac (Chevrolet style) 12 bolt as far as anything I've ever seen or experienced, and he says he has a 12 bolt.

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1966 Strato Chief 2 door, 427 4 speed, 45,000 original miles 

1966 Grande Parisienne, 396 1 of 23 factory air cars (now converted to a "factory" 4 speed)
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Cheviac


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yard count 2016 127.JPG



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Cheviac


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283 glide twelve bolt 3:36 only one I've found other than a 67 SS impala 327 four speed car I once owned

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4SPEED427


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My black 66 Grande Parisienne was a 283 glide with 3.31. I think 283 glide 12 bolt full size were mostly 3.31 but maybe in 67 that changed.

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1966 Strato Chief 2 door, 427 4 speed, 45,000 original miles 

1966 Grande Parisienne, 396 1 of 23 factory air cars (now converted to a "factory" 4 speed)
seventy2plus2


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Carl Stevenson wrote:

Well, 3 and 1/3 turns seems pretty close to 3.31 according to what my math teacher taught me...

Unless your math teacher taught you that 3.07 is closer to 3 1/3 than 3.31!!!

 Strange thing is that he said he turned the rear wheel 2 full turns (not 1), and the driveshaft turned 3-1/3 times.   



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4SPEED427


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Whoops, that was me speed reading again, I missed that. That can't be right.

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1966 Strato Chief 2 door, 427 4 speed, 45,000 original miles 

1966 Grande Parisienne, 396 1 of 23 factory air cars (now converted to a "factory" 4 speed)
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66 Beau


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non-posi rear, with only one wheel turning...

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davelacourse


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66 Beau wrote:

non-posi rear, with only one wheel turning...

So, still close to 3.33 (3.31 or 3.36, your choice) rear end wink

And, just pull the rear cover and count the gears and you have a definitive answer, eh? biggrin

Needs new gasket and lube anyway, right?

Dave



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56Pontiac  1956 Pontiac Pathfinder 2dr sedan, 496 - dyno'd 545 hp, stick shift, 4.11 posi - Hot Rod

  1964 Acadian Beaumont SD convert, 283 - factory 195 hp, Powerglide, 3.08 10-bolt - Cruiser

  2012 US-built crew cab truck - Daily Driver and Boat Trailering
Bago


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Hello Lads,

Right, I've been under the car and cleaned the section of axle where the code is supposed to be and, well, see for yourselves......

www.flickr.com/photos/35630959@N07/30868688852/in/dateposted-public/
www.flickr.com/photos/35630959@N07/30868685642/in/dateposted-public/
www.flickr.com/photos/35630959@N07/30949777806/in/dateposted-public/
www.flickr.com/photos/35630959@N07/30949776356/in/dateposted-public/


However, I did find another code, on the other side of the pumpkin, this mean anything?

www.flickr.com/photos/35630959@N07/30868687512/in/dateposted-public/


Thanks again for your help on this! Once we've sorted it out, I'll let you know why I need it. Don't wanna let it go just yet or it'll take the thread off on a massive tangent for sure!!

Oh, I don't suppose it matters that mine is a RHD export model by any chance does it?

Cheers
Ian
(U.K.)


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