help decode my 12 bolt..

1519 Views 11 Replies 4 Participants Last post by Dan1979, Mar 13, 2011

Dan1979

Discussion Starter · Mar 12, 2011

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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Mike

· #2 · Mar 12, 2011

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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Mike

· #4 · Mar 12, 2011

Yeah ,that should be a 69 C-type rear but your R8 code for 69 shows an O-type rear.
As I said ,pull the cover and have a look see.

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Mike

· #6 · Mar 12, 2011

Does it have c-clips?

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Mike

· #9 · Mar 12, 2011

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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Mike

· #11 · Mar 13, 2011

I'm figuring there's a misprint with the 68 & 69 Olds codes being swapped.
Doesn't make sense to have the R8 being a C-type for 68 but an O-type for 69.
http://www.442.com/oldsfaq/ofdif.htm
Hollander Interchange shows the same info for the R8 code.
Chevy didn't use a code similar to R8.
Might be why you got it cheap if the owner saw the O-type code for it.

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