Why didn’t these rear ends get the aftermarket support of the other GM differentials? From what I understand, the ring gear is basically the same size as the 12 bolt Chevy axle, the axle shafts are larger and are bolt in (no C-clip eliminators needed) the carriers supposedly don’t crack like the Chevy carriers do, and they seem to be easier to find. I paid 100 bucks for my chevy 12 bolt 30 years ago (that would never happen today!) but you can’t give away the type O diff. Just curious.

 

For starters, they were produced for a very short time (1967-1970) then were replaced by the corporate 10 bolt.

The O-Type ring gear is around 8.5", not 8.875 as the Chevy 12 bolt.

As for carriers, I recall a guy in town back in the 80s that had to replace the 3.91 O-Type in his 1970 W-30 4 speed because he cracked the carrier at the drag strip. He put in a Chevy 12 bolt and had no problems after that.

The axles are larger only on the early 67-68 versions with HD 31 spline shafts (found on 3.42-up ratios) - all of the others were standard 28 spline shafts that are the same diameter as the later corporate 10 bolt 28 spline shafts (different spline angle, though, so not interchangeable).

 

So the bolt in axles are the only real advantage? I thought the axles were larger for the entire production run. And I thought the O axle was used from 64-70. Learn something new daily!

 

The Type O was actually released in spring of 1966 and used through the end of 1970 model year production. As noted, they were only used on Oldsmobile A-body cars, so the market for customers is miniscule and not worth the production costs for manufacturers who have to make a profit. The 8.5" ring gear held with ten bolts is not the same size as the 8.875" ring gear held with twelve bolts as used in the Chevy 12 bolt axle. The bearings are different sizes, etc, etc. It is interesting to note that while there are only ten bolts holding the ring gear to the carrier, they are larger than the 12 used in the Chevy axle and can actually carry a greater shear load in total.

 

As I understand it there was a Detroit Locker unit produced that will fit the O type rear. These are very rare and I do have one in my Olds rear thats in my 67 442 vert..

 

These days it costs about the same whatever you build, if you are going for very high strength, because of aftermarket parts being priced similarly for the different diffs. However, you may not be able to get something you particularly want, such as a Detroit Locker, for a 12 bolt vs. the Type F Dearborn rear (lol, Ford 9"). I have a 12 bolt with welded tubes, Mark Williams axles, steel bearing cap, Moroso posi that was under one of my W30s. The other has a Type F with aluminum center, DL, 35 spline Mosers etc. It all depends what you want, so long as you choose from those two or the Strange Dana 60, all are available in bolt-in form at various levels of strength.