I have a 70 SX that has a 12 bolt and need to find out whether it is a O type axle. Any help would be appreciated.

 

It's a Type O.

Seriously, unless the car was built in Canada or the axle has been swapped, it's a Type O. You can tell by looking at the rear cover on the axle. If it's smooth, it's a Type O. If it has an inverted "V"-shaped ridge on the cover, it's a Chevy 12-bolt.

 

And to clarify: It is actually a "10 bolt rear" which means the carrier is 10 bolt, but the cover is 12 bolt. It's the carrier bolts that count, not the cover bolts.
And there are 12 bolt rears with 10 bolt covers just to keep things confusing!
The "O" rear is best referred to as the "O" rear, because of the difference of carrier and cover bolts.
FWIW, the Chevy 12 bolt is 12 and 12.

 

Thanks and now the second question. I want to have a posi O axle carrier installed and was told Super Cars Unlimited is the where to purchase it though I need to know what gears I have in the differential so I can get the correct carrier. How can I get that information?

 

Pull the cover, (it's full of gear lube, so have a container to catch it) on the side of the ring gear it should have the ratio, you'll see something like 42:13 for example stamped on it along with "GM" and a few numbers. The 42:13 is what you want, 42 teeth on the ring, 13 teeth on the pinion, which, in this case is a 3.23 gear set. You probably have a different set. Take a look and tell us what you find.

 

I went this route just a few months ago. https://classicoldsmobile.com/forums...do-i-need.html
Pay attention to post #21 with the codes to ID the stock gear set in there.

I discovered that buying USED carrier and gears for this Faux 12 bolt is nearly $1000. :screwy:
That's not including paying someone to put it together unless you can do it yourself.

Just a consideration, but I put in a Chevy 12 bolt with way more for way less.
Just depends which is more important to ya, keeping it Olds, or keeping more $$$ in your wallet.

 

Parts for the 12-bolt Olds rear are scarce,thus costly.New carriers are $525.00,new ring & pinion seats are almost $300.00,then all of the bearings & seals to do the whole rear are $125.00. It adds up quick. With a 12-bolt chevy,some of the parts are cheaper,but the rearend housing itself is more,due to the demand vs availability. It almost comes out as a wash between the two.
The cheapest alternative is the 71-72 8.5" 10-bolt. the cores are cheap,the parts are readily available,& cheaper than the O-axle,& they are plenty strong.You will need to shorten your driveshaft to install this rear,but even with that cost considered,you will still be less than the O-axle rebuild,or buying a 12-bolt Chevy,unless you can find someone selling a decent one,or is willing to take a loss,& make it your gain.

 

I can't even GIVE my complete Olds O rear end away for $300......and I'm in the Chicago burbs.....big market.
So be aware before you spend $1000+ on just parts to upgrade it.....not including the labor to put it together.

They are only made 1967-1970 so they are rare which = wallet bleeder
They are NOT desirable which = no ROI , Return on Investment

It's definitely true that the 12 Bolt Chevy market is MUCH bigger and desirable.
Parts are abundant and cheap, and you can pick up a 12 Bolt core cheap usually too.
I got lucky and found mine after just 2 weeks of looking.

I ended up searching all the Chevy sites and found a guy selling a FRESHLY built 12 Bolt Chevy
with Eaton Posi, 3.73 Richmonds, 31 spline Strange Axles, Timken kit, 1350 pinion yoke, and a Moser T/A Diff
Cover for just $1000. He even tossed in the Baer Street 11" disc brakes with D+S rotors for nothing extra. ($1100 setup alone)

He upgraded his 71 Chevelle to a 9" Ford, so he wanted it gone. SOLD!!!
Point is, deals are out there to be had. If I ever decide to sell my rear end,
I will make my money back and then some. With the O axle, I'd lose big time.

Olds12BoltDiscBrakes3.jpg

 

That depends on the gear ratio and whether or not it's posi. You're right, a 2.78 open "12-bolt" Olds rear is not worth much, because 1) there's so many of them out there, and 2) most people want posi and lower gears, which means shelling out big bucks for the parts you were talking about.

If the rear you're trying to give away is a 3.91 posi, please let me know. I'll be happy to take it off you hands for $300. Heck, even if it's a 3.08 or 3.23 posi. That posi carrier is probably worth $300 alone, since that's what the Richmond 3.42 and 3.90 gears are made to work with.

 

Here's a guy in 2006 selling one with the 3.90's for just $350
If it was so desirable and $350 being a steal, it shouldn't have taken 2 years for the 1st reply.
https://classicoldsmobile.com/forums...-rear-end.html

Good luck in your search!!!!

 

The guy selling a 12-bolt O-axle 3:91 posi was giving it away.They are worth much more than that,even if they are not rebuilt.Even if the housing was all pitted-up,the posi unit & gears are still worth more than that.If I was on here in 2006,I would have bought it,even if if I needed to freight it.I'd still be ahead.
You were in the right place at the right time when you got that Chevy 12-bolt with the rear discs. That goes along with the last sentence in my previous post.

 

Guess I might have a buyer for my Old O axle in a month.

I might not even list it anymore if that's the case.

 

Listen to Brian (507olds)! On a budget for a street car, or low powered strip car, the 8.5 ten bolt is a good way to go. If you want strong for slicks with a 4 speed, etc. you will spend a lot more, about $2500-3000 regardless of whether you want a 12 bolt, Dana 60, or 9" Ford, each with the good parts. If you want a 12 bolt or Dana S60 (from Strange) new housing with the tubes welded to the housing, you are getting new aftermarket axles, and either an Eaton, Dana, or Detroit Locker (the latter for 9" and Dana only). You can get the S60 with ears to make it a drop in, and Quick Performance and others weld ears to new or used 9" housings so they drop in also. If you want bulletproof, you are going to spend money. If you want cheaper, be careful because the axles aren't real strong on the 12 bolt C, or the type O. The 9" 31 spline axles are decent but rare.