jerseyjoe

Hi All,

I found S3 stamped on the back of the passenger side axle tube and a limited slip tag on the upper differential bolt as well.
Research shows a 2.78 limited slip type O differential.

Can someone confirm gear oil weight? Guessing 80w-90?

Also if I wanted to swap to 3.23 gears what needs to be changed other the the ring and pinion gear?

Thanks, Joe

Indy_68_S

For the gear oil weight, 85w-90 seems to be preferred.....Unless, of course, you're in Alaska or Siberia or something like that...

https://classicoldsmobile.com/forums...pes-rears.html

For the gears.... the 2.78 uses a different carrier (673) than the 3.23 (671).......
...so you'll need a new carrier.

For more info search for posts in this section by 507OLDS (Brian Trick) or monzaz(Jim)...These guys are gods of Olds rearends.....

507OLDS

In the past,I have machined ring gear spacers for the O-axle carriers,to make the # 673 carrier usable with the new Richmond gears,or the GM 3:08/3:23 gears.The ring gear journal on the carrier is wide enough that you can mount the spacer,and still have enough for the ring itself to press onto,which is critical in keeping the ring gear centered,and keep it from deflecting.You don't want it floating out in space.That is a common problem with the 12-bolt Chevy spacers,and that is why so many of those with the spacers fail.
If you are going to go that rout,get a set of Richmond 3:42's.That is a good all-around gear.A spacer kit is $55.00 plus the shipping.It includes the spacer,and either right-hand thread bolts for 67-69 O-axle,or left-hand thread bolts for the 70 O-axle.
If this is a mild build,or cruiser car,you will be fine,but I would NOT recommend any type of spacer set-up,in any rear,for an application with a bunch of blunt force being applied to the rear,like a big block,stick shift,trans-brake,slicks,etc.

jerseyjoe

I'm in Jersey does that count
Of course they are different carriers! That would have been to easy

Brian, Thanks for the information, that is great to know. Definately a mild build for now. Down the road I may look at working the 350 and adding a 350 trans but got lots of basics to take care of first.

Joe

68oldscutlass

Looking to do EXACTLY this. Jerseyjoe, did you ever do this? 3:23 impossible to find right now so ill go with 3:42. They sell the spacer kit through same company??

monzaz

LOL. All Olds 12 bolt gears are impossible to find right now. NO aftermarket gears at this time till some time later in the year ...I HOPE. Jim

507OLDS

This post was from 2 years ago. The situation is a little different right now. There are over 150 orders for new O-axle gears,but they still have no idea if or when they will make them.

jerseyjoe

Hi Guys, Yeah old post. Still have the 2.78 limited slip. Still considering the swap but obviously with the lack of parts, not right at this moment. I did swap out the jetaway for a turbo 350. Obviously that helped. Surprised somebody has not reproduced them by now. Guess supply and demand.....

monzaz

That is not the problem. One company bought out another company. So they have to do all the BS that goes with figuring what to carry or what stock is leaft or which way to go with everything. It will be a year yet. Jim

507OLDS

What makes the most money,gets made first.