Was in a 65 gto, bought it a bit rushed to put in my 66 lemans. Thought it was a chevy 12 bolt, then figured out its an Olds 12 bolt cover with 10 bolt internals. Gearing is 4:11, little higher than what I wanted. It's been all rebuilt. Looking for $1500. Just want to get back what I bought it for. Can post all #'s on housing l a tater.

 

Where are you located?

 

Newington, CT

 

4.11 wasn't a factory-available gear ratio for these Type O axles. 3.91 and 4.33 were the closest. There have been aftermarket 4.11 gear sets made over the years. Is this posi or not?

 

You are absolutely correct , went out there and it's 9/39 4:33, h
guy told me it was 4:11, the I opened cover and verified

 

Wow, 4.33 was one of the high performance factory ratios. I’m guessing this is a Heavy Duty 31 spline axle version.

 

I’m shocked that Joe did not correct the “posi” verbage. 😁. Olds-speak would be anti-spin.

 

He's a GTO guy, not an Olds guy. I figured I would translate.
(Yeah, I know posi isn't the correct Pontiac term either...)

 

Back in my day, u just referred to posi or non posi. But yes, as I have been doing more research, I should say "anti-spin". Just did some scrubbing and axle code is TW

 

Pics of codes

 

PONCHO ==== SAF-T-TRACK

They had 10 bolt cover
With 3.55 or bigger # ratio DEEP Gears housing has a large N (nodular) cast on top of the center section
The "posi Unit" was a 4 pinion
Hard to find parts for in the 1980's when I played with them

 

That is correct, but at 19 or 20something, you didn't go around asking if they had a saf t track in the car...it was a posi!

 

Factory installed unit not a dealer installed unit.

 

My brother had a 1967 Firebird
He showed me the tail lights more than once
Quick in short distance BUT on top end he could be beat

He was an "artist" so he painted POSI in BIG silver letters on the axle
Soon after clutch burned up and that little MEAN green car got sold

 

Just thought I would put it out there, if no takers, I'll pony up the $430 and get the 3:42 or 3:90's and keep it.

 

IF you head on highway the 342 will make some high speed bursts
easier on you racing fuel bill

 

There are some peep holes that will pay for 433 gears
Keep the Shiny Side UP

 

Yea 3:42 much easier on hwy and gas bill but 3:90, so much more fun! I'll definitely save those gears if I end up keeping it. Guess I have a stupid question, if internals are a 10 bolt, why can't I use plain old BOP gear set?

 

^^^THIS. That's a pretty rare and valuable unit, but really only to someone who needs it for a 68-69 W-30/W-31 resto, so the market is pretty small. Fortunately, my 68 W-30 already has one.

 

Because they are two different rear axles. The main reason is they just won't interchange.

 

To add to Mike's response, different ring gear diameter, different bolt circle for the ten bolts, different bolt size, different ring gear offset from the pinion centerline, different bearings, etc, etc. In reality, the only thing they have in common is the fact that there are ten bolts holding the ring gear to the carrier. Both the 8.2" BOP axles and the 8.5" Chevy axle use ten bolt ring gears, but nothing interchanges. Also note that you have a four-series carrier, so the aftermarket thick gears that have been made for the Type O won't fit, since they are designed for the three-series carrier. You can only use OEM gears for a four-series.

 

I didn't feel like posting all that.

 

Understand. I often feel the same way.

 

Thanks for all the info guys. For what it's worth Olds has some pretty sweet machines, if I hit lotto, would Def put a 442 in my stable to represent the breed. The rear is probably the last item I'm going to tackle, so I have some time.