This is in my 70 GS 455, it has 12 bolts on the rear cover, has the 8.5" ears on the bottom, but is not obviously a 10 bolt 8.5 Buick rear. I couldn't find any axle codes on the tubes or casting numbers on the lower bottom pumpkin that Chevy 12 bolts have. The only casting number is on the front of the pumpkin centered underneath which says CFD4. Here is a pic. Seems to be around a 3.08 ish ratio non posi. What rear end is this?! Olds? Would like to get a limited slip in this thing.
Well, never mind , just found the casting number. It's a 1970 Olds/type O 12 bolt 402227 was the code on it. Still can't find the code on the axle tube, but one rev of the wheel spun the driveshaft a little past 3 turns, so prob 3.08 or so. Should be fun getting a posi for this thing!
The 12-bolt O-axle rears have the code on the backside of the passenger side axle tube. 2-digits. It is either 2 letters,or a letter & a number. That casting was used in 69-70.
Yeah, Olds tried to trick everyone in thinking they had a true 12-bolt rearend. You can sell it to a 442 guy. They'll go nuts over it. A "good" 12-bolt for an a-body will run anywhere from $1000 to $2000, depending on it's condition.
If you need the correct rear for your 70 GS,I have one. A 70 3:42 OO-code with all new parts. If 100% originality is not a concern,get an 8.5" 10-bolt,from a 71-72 Skylark/GS or Cutlass/442.
Some Canadian GS's had the Olds 12 bolt rear. It's not a bad rear end and if you are concerned about originality I'd keep it. The next owner might wish you had too. $$$$$
I read in the 70 Buick assembly manual and I have had 2 70 skylark's from Framingham Mass. Plant With 12 bolt Chevy's. They only came in 256 no posi.they even put a different axle snubber in the center of the frame for the 12 bolt
That's how I would pluck a lot of cores throughout the years,at the local junkyard. I would check all of the 68/69 Skylarks & 68/69 Cutlasses,and see if they had MADE IN CANADA on the cowl tag. Then I knew it was a 12-bolt Chevy. They didn't come with the O-axle in either one of those cars. I did part a 70 Skylark post coupe,from Mass,and it did have a 12-bolt Chevy,so maybe there is some truth to that. I just figured it was swapped at some point. You can also find some 12-bolt Chevy rears under 69-72 Gran Prix's,but not all of them,
Well sure, of course... I am in Little Rock AR. I've looked and didn't see made in or for Canada anywhere on the cowl. Likely it was swapped after one too many clutch drops or something LOL. Car was well kept but definitely owned by someone who loved the car and kept it garaged and did small mods; chromed a bunch of pieces in the engine bay and installed an old school Mallory coil, plus it was a stripper model GS 455 with bench, no power accessories, no air, and 4 speed.
What gear ratio is in that Olds 12-bolt? Is it a posi? If you are unsure,the 2-letter code is stamped on the backside of the passenger axle tube.That will help identify it,unless someone went in & swapped the guts.
They also had a 2:78. Here are the codes for numerically lower gears and no posi: R2 = 2:56 SA = 2:78 SC = 3:08 SE = 3:23
