camdon454

I picked up a 70 Cutlass S a few months back, and was surprised to find a 12 bolt underneath. I thought it was obviously an upgrade over the 10 bolt, but I've read otherwise. Can anyone explain?

droptopron

Standard rear in '70 was a Type O with a 12-bolt cover but a 10 bolt ring gear. Don't get too excited. it could very well be a 2.73 one wheel peel.

jfb

does yours possibly have a line in the cover for oiling purposes side to side,If yours does then you have a chevy 12 bolt with c clip axles if not changed beforehand.

droptopron

I thought US cars got a Type O & Canadian cars got Chevy 12 bolts?
A Chevy cover has a ridge in it & a type O is smooth.

oldsmobiledave

He said it was a 1970. No Canadian built cars after 1969 so if there is a 12 bolt Chevy under it then it is not original.

camdon454

camdon454

The rearend is original, not a Chevy. Definitely one wheel peel though! I've seen limited slip, or posi kits offered in OPGI, but they are all for 10 bolt. Anything similar for mine? Or should I just look for a new rear? The car is all original and I'd hate to start changing it out to accomadate a few more ponies.

Qwik71442

SuperCarsUnlimited and a few others who visit this site sell the 67-70 12 bolt Type O Posi

joe_padavano

Just to clarify, "12 bolt" refers to the number of bolts holding the ring gear to the carrier. It is just coincidence that the Chevy axles have the same number of bolts on the rear cover. The Type O does not. More importantly, the Type O uses an 8.5" ring gear held on with ten bolts. The Chevy 12 bolt uses an 8.875" ring gear held on with 12 bolts. Interestingly, the ten bolts on the Type O are larger than the 12 on the Chevy axle and can actually transit a higher torque to the carrier. Of course, other factors like the gear diameter, bearing size, etc also contribute to total axle strength.

redoldsman

This comes up so often that maybe Type "O" should be referred to as 12/10 rears or 12 bolt cover rear ends. This has to be the umpteenth time this has been clarified. It is part of the Olds education process. We all learned it at some point.