1BAD68"S"

ok ive counted the bolts on the cover and the count is 12 but i have yet to locate the code on the axel to tell me for sure what "stock"ratio the car came with because you never know if the original owner changed but from what ive gathered the most common is a 10 bolt. now i know the 12 bolt is stronger but is the diff cover the way to tell or is it the number of ring gear bolts? i need a solid answer because i will be attempting to source a posi unit and rebuild kit (still not sure if its a blown up posi or a peg leg)please will one of the all mighty oldsmobile gods help me before i order the wrong stuff

Oldsguy

An Olds 12 bolt is not necessarilly the same as a Chevy 12 bolt and may not have the same reputation. There is a number stamped on the axle, facing forward on the passenger side which can be used to identify it. I need to do some research on this and promise to look it up. Sorry I don't know it by heart and am not well versed on this subject but do know for sure about my first statement. Hope I can get the info you need.

I found this link, hope it helps:

http://www.442.com/oldsfaq/ofdif.htm#Differentials

Eightupman

I am thinking that the 10 or 12 bolt designation comes from the number of bolts that holt the ring gear. I have been told that some can be identifed by the SHAPE of the cover, but not 100% sure on this.

John

Oldsguy

Both, but on the Olds the 12 bolt cover doesn't mean 12 bolts on the ring gear.

Redog

Is the RPO tag still in the car? Typically it's a GU? that will tell you the gear ratio.

I went from a 2.73 (GU2) to a 3.42 (GU6) in the Delta's rear end

1BAD68"S"

ive degreased the tubes the best i can but its time to break out the wire brush...like i mentioned i have only identified the cover bolt count at 12 but i dont want to pop the cover just yet(afraid to) oh well ill try and find it but a solid answer to what makes them different is what intriges me

rockethound

the o type olds has a 12 bolt cover, you have to take it off and count the ring gear bolts. the diff ratio code are stamped on the right inboard side of the axle housing tube and it dosn't tell you how many bolts are on the ring gear, all that code will tell yu is is weather it is a c type or a o type and the ratio and std or anti spin. you get the code off the axle tube and i can tell you what it is. one way to tell if you have posi is jack the back of the car up so both rear tires are off the ground and turn one tire while turning look under and see if the other is going the oposit way or turning in the same derection, if going the same way you have posi. i've blown up o type rear ends and have had better luck with c type.

1BAD68"S"

well i thank everyone but the code mystery was solved with a can of pb blaster and a wirebrush....drum roll....its a code "SA" 2.78 ratio pegleg.....and from what rockethound has said i think i will be looking for a stronger rearend. i have a friend that has a fresh "true" 12 bolt for his 70 chevelle but he is instead going with a narrowed 9 inch and he owes me some money so you can probly see where im going with this,will the "chevy" rearend fit without problems(other than a hybrid u-joint)cause ive already looked for a rebuild kit for my stock "o" and the pickens are real slim....oh well...anyone want to buy a stock rearend for a 68 cutlass??

rockethound

hey it should fit like a glove, all a arm mounts are the same.
one of my buddies runs a built 455 a turbo 400 and a 12 chevy, he runs 12seconds so they hold up pretty well he also tore out his o type rear end.

z11375ss

12 bolts are tough stuff. I've run them behind some serious horsepower and no problems.