My car is 69 Cutlass with Single Track Type "O" - No show car status
Looking to economically upgrade to posi for my Cutlass, the 69 Cutlass now has a motor being from a 1970 Olds 455 with Muncie M20

Searched & cleaned (like 5 times) but NO axle code to be found
So I wanted to check the ratio

Jacked up the rear end and rotated just one non posi tire 2 times -
and the drive shaft rotated 6 1/4 times
So my rear ratio is 3.23 (?) YES ?
I read here that the "O" type 3.23 is a 28 spline set up

and I found this posi unit that should be a direct fit in as a replacement to give me posi

Here is the 2 units

https://www.ebay.com/itm/68-72-Oldsm...ry!01985!US!-1

https://www.ebay.com/itm/68-72-Oldsm...oAAOSwO7pcad6t


Your comments / suggestions / recommendations much appreciated
Thanks
C

 

Recheck your count. A 3.23 would have been about 6 1/2 turns. A 3.08 would have been about 6 1/8 turns. I'm betting it's the latter. Those posi units should work if the vendor has the application correct. Of course, the Type O axles were made from 1966-1970, so the fact that they say 68-72 would indicate that they are less than fully versed on the intricacies of Olds rear axles.

 

yes

My error

I posted wrong from doing it too many times

my 1st post should have said 4 tire rotations = 6 1/4 drive shaft turns
I just redid it
2 tire rotations = 3 1/8 on the driveshaft
so thats a 3.08 and still a 28 spline ?

I'd be happy with either 3.08 or 3.23 and his web page says either is a direct replacement using my ring & pinion (?) Yes ?

How sturdy is my existing unit ? Will my housing and or the posi I could install take abuse ?
Or should I just seek a complete used Corporate 12 Bolt posi "A body" from 68-72 ?

I agree with his mis posted info about years - I saw that too
I'm going to call him tomorrow (Rons Machining Service) and ask a lot of questions ...

800 694-3098

Thx for you input


His Web Page does say

[font]Application: 1968-1972 Oldsmobile Cutlass & 442 GM 8.5" "O" Axle[/font]

• [font]Cover Bolts: 12[/font]
• [font]Ring Gear Bolts: 10[/font]
• [font]Axle Splines: 28 (must check)[/font]
• [font]Pinion Splines: 27[/font]
• [font]Compatible Gear Ratios: (Factory 3.08-3.23) (Richmond 3.42-3.90)[/font]

[font]Package Includes the Following:[/font]

[font]1- GM 8.5" Olds Clutch type Posi LSD (28 Spline)[/font]

[font]1- Bottle Posi Additive[/font]

https://www.ebay.com/itm/68-72-Oldsm...ry!01985!US!-1

 

Yes, yours has 28 spline axle shafts.

Yes, those aftermarket carriers are made to fit the factory 3.08-3.23 gears.

My understanding is the O-Type is essentially as strong as the later 8.5" corporate 10 bolt. What are your plans for it, as in how hard do you plan to drive with it? The one under my car has survived a lot of spirited use over the past 35+ years.

I don't know what a "Corporate 12 Bolt posi "A body"" rear is. I am familiar with Chevy 12 bolts and corporate 10 bolts.

 

Again my error about Corporate (new to me stuff) - thanks for correction

My use is just local use, no long trips or 1/4 mile track, and leaving some spirited black marks here or there,
so the 1969 Type "O" 12 bolt in mine converted to posi should be strong enough -

and there are some 1970 and up Corporate 10 bolts posi A body complete units in my area for sale as well, as well as the more expensive 68-72 A body 12 bolt (Chevy) posi's as well

so NOW I'm seeing many choices for my rear end posi upgrade

Thank You

so I'm learning and shopping

Thx