on cutlass,s 68 to 73 0r more why would a 70 cutlass have a 12 bolt cover and a 442 have a 10 bolt cover sounds backwards to me please explain

 

68-72 was available with 4 different differentials.

1. most common is the type o rear. 12 bolt cover with a 10 bolt 8.625" ring gear. this is technically a 10 bolt despite the 12 bolt cover. These came in the 68-70 models.

2. chevy 12 bolt. came on Canadian cars.

3. GM corporate 8.5" rearend. 10 bolt cover, 10 bolt ring gear 8.5" diameter. These came standard in the 71 and 72 models

4. W-27 rearend. which is a type o with an aluminum center section.

 

Well, the first problem is that you need to understand that the number of bolts on the cover is meaningless. The "12 bolt" Type O axle used under the 1966-1970 Oldsmobiles is NOT the same "12 bolt" axle used by Chevy. The Chevy axle has 12 bolts holding the 8.875" ring gear to the carrier. The fact that there are also 12 bolts on the cover is purely coincidental, as the "12 bolt" refers to the ring gear bolts. The Type O uses ten bolts to hold an 8.5" ring gear to the carrier, the same as the "ten bolt" Corporate axle (although the actual ring gears do not interchange). The fact that the Type O uses 12 bolts on the cover is meaningless. All Cutlii/442s after the 1970 model year went to the Corporate 8.5" "ten bolt" axle, which as you can see above, was not a downgrade from the Type O. Also, as noted, Canadian-built Cutlii/442s through the 1969 model year actually did get the Chevy "12 bolt" axle. This was due to convenience, not any "high performance" issue

 

Thank you sir for explaining it to me

 

....and now I know too. Thanks!
Damn Joe, you sure know how to answer a question!


Slight hijack but on topic:
Are all "12-bolt" rears in '70 442's type-O? Did any receive the Chevy 12-bolt?

 

Since there were no Canadian production of Cutlass after 1969 (69 was the last year at Oshawa) it would stand to reason that all 1970 12 bolt rear ends in the Cutlass line up were Olds only - not Chevy.

 

Which is why I said this:

 

Joe, my response was about 1970 442's, not 1969. Your response was specifically aimed at 1969 Canadian built 442s? Mine was more of a direct answer to the question he asked IMO.

 

My 72 cutlass has a 12 bolt chevy axle. I would guess more than a few chevelle rears have been installed in oldsmobiles 1970 and later by owners wanting to change from the factory offering.

 

I was wondering what the ring gear size was for the 10 Bolt O type rear end. J-(Chicago) lists it as 8.625 and Joe_Padavano lists it as 8.50. Thanks.

 

but they are strong rear ends right ?

 

Every factory reference I've ever seen calls it 8.5, but it really doesn't matter. The 8.5" "corporate" axle gears do not fit. Also note that GM has alternately referred to the 7.5" axle as 7.625", yet the gears and parts are the same.

 

I wrote my answer the way I did because Olds stopped making A-bodies in Canada after the 1969 model year, so by definition, no 1970-later cars came with the Chevy axle.