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Discussion Starter · #1 ·
just picked up a 12 bolt open drum to drum for 300.. Real nice no rust at all. I already determined its a 69 rear but can't figure out the other #'s . They are R8 0903K. Any help would be great.. Also how do i figure out gear ratio thats in it? Is there numbers that tell that?... Thanks....Dan
 

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If it's actually a 69 rear it's a 1969 Olds O-type 2.56 open carrier.
Get the casting number and date as the R8 code in 68 was a C-type rear.
Built Sept 3 at the McKinnon Industries plant.
Remove the cover and see what's actually inside.
After 42 years it could probably use an oil change
 

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Canadian and US built Chevy's used the same code.
Your housing is a GM A-body 12 bolt but the code comes back as Old's.
I'm seeing the R8 code for 69 as an o-type rear and for 68 as a C-type rear but sometimes that's not always the situation.
As you now have the cover off ,take a look at the axles inside the carrier and see if there are c-clips in there.
 

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It is probably a 2.56 geared Chevy 12 bolt. R8 shows to be a 2.56 gear for the Oldsmobile type 12 bolt and they may have used the same code for the same gear ratio on the Chevy rear. On the O type 12 bolt it has a 12 bolt cover that is smooth with no eyebrow at the top and the ring gear is actually a 10 bolt.
 

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Discussion Starter · #12 ·
No he hept all his o type rears as he owns a restoration shop and specializes in oldsmobiles.. When i asked him he flat out said he's not into chevys.. It is a 12 bolt 69 rear with a 12 bolt ring gear and 2.56 gm gears.. Thanks everyone for the help..
 
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