I agree with the 9 3/8 in that pic. But Monaz is the real expert. Interestingly, if you look at Group 5.529 for the 1975 model year, it says that if you E body has a "P" axle you have the 8 7/8 " gear set. But if your 75 E body has a ""O" axle you have 9 3/8" a gear set.
I've asked board member "75Riv" (Rob) about this, and he said that both his 1975 Rivieras came with the 8 7/8.
Yes 9 3/8 OLDSMOBILE full size rear. It is a 'S' spring posi and most of the rears we run across only have 2.56 2.73 I have a Posi for one 2.73 but no gears . 3.08 3.23 3.42 I think were available. You can find these units all the way back to 1967 Olds 88 98 etc. They were used as the BIGGEST rear in the 1971-1976 full size car models. IF you had a WAGON or a SEDAN with a Big BLOCK you got this rear. Pontiac rear 10 bolt cover 12 bolt guts 1971 -1976 was reserved for the mid powered FULL SIZE CARS And finally the low powered Impala and other BOP car standard option was the 8.5 10 bolt rear. Still might make more sense to get a smaller 10 bolt 8.5 as you have more gear options and posi unit pretty available and with a 30 spline up grade could still take some punishment. Jim EXTRA INFO The thing here you have to understand is that EVEN though the ring and pinion in the full size cars are BIGGER. The posi units GUTS are still all the same parts. NOTHING IS BIGGER???? Weird huh? IE - The FULL SIZE 9 3/8" Oldsmobile rear posi unit shares the same clutches and spider gears as the mid size 12 bolt olds (10 bolt guts posi unit parts) SO- really the only thing that is bigger is the ring and pinion to bleed off heat from the extra weight of the car ...more weight MORE FRICTION!
i went and seen the rear it is a 2.93 posi rear apparently for the full size 71-76 big cars i did not buy it but will start a thread showing where it is and the price jake
the guy that owns the rear swears it came out of a 76 buick riv........ i don't know but you should ask monzaz as he is the rear guru........ i was under the impression that they would interchange but the riv is its own animal........ jake
For 71-76 I think a 9 3/8 from an Olds or Pontiac will interchange. Buick 9 3/8 rears from 1970 Buicks and earlier are a different 9 3/8 that are Buick only. I think this may be a point of confusion.
Pretty sure the Riv has the same 4 link suspension as the 71-76 full size cars. GM made all the full size cars the same and all interchangeable. The riv was on its own on alot if stuff BUT I think it still has the same as all the rest up till 1976. 1977 EVERYTHING changed on the CArs full size was NOT full size anymore...lol. I just received a posi 12 bolt 93/8 2.93 posi today also. Weird huh? Mine is also for sale as is right now. ' these OLDS 9 3/8 were the strongest rears of the era and were reserved for 455 and wagon cars. Buick Olds And Pontiac Please reread the previous post as i went over this for you already. If your riv has 2 upper control arms and 2 lower control arms i am sure the rear will fit. 1971-1976 electra, LeSabre, Estate etc. Jim JD
This is for sale - I thought it was from a 74 it is all boxed up ready to ship $275 for it plus shipping from 45214
That will fit all 1971-1976 12 bolt Olds rears. This posi unit is 31 spline and should fit the 2.73 2.93 3.08 ratios 761 casting 455 FULL size cars got this optional rear end. Buick Olds And pontiac. 455 cars Wagons also got this 9 3/8 rear. 10 bolt cover 12 bolt gut rear was a PONTIAC full size rear and 31 spline bolt in axle which all the 350 and 400 mid powered cars received. 10 bolt 8.5 was reserved for Chevy and low powered full size base cars.
Guys, can anyone identify this posi carrier? Excuse the poor photos: it's on a shelf overhead in a retired mechanic's garage, who brought it home from work in 1973 (if he is recalling correctly). This was installed in a full-size GM car that was new at the time: the lady owner wanted the limited slip removed and it was replaced with an open carrier. He brought the barely-used posi-guts home from work. Again, I'm unsure if this story is exactly correct or true. It is in a GM box with markings too faded out to read. After hearing it was out of a full-size car, I was going to buy it for my 1971 Riviera with open rear axle and 2.93 gears, but have since found thanks to monzaz's wonderful and informative posts that not all full-size GM axles were the same during this time. I have read my axle is a Oldsmobile-designed 9 3/8" 12-bolt unit. The photos I've seen posted of what these carriers should look like (including in this very thread), look different from this posi that is available locally. Can any one confirm what it is? I also own a '75 Pontiac Grand Ville Brougham 4-door hardtop with a 455, which I believe has the Pontiac 8.875 10 bolt cover, 12-bolt guts rear axle. Maybe it would work for that? If it's just an 8.5 Chevrolet carrier, I think I'll pass. Thanks guys! -Josh Noiles Nova Scotia, Canada Untitled by Josh Noiles, on Flickr Untitled by Josh Noiles, on Flickr Untitled by Josh Noiles, on Flickr Untitled by Josh Noiles, on Flickr Untitled by Josh Noiles, on Flickr
Can you at least do some work and pull it from the box? Please? We need to see the spring pack and the casting number if you can. We also need to see how many ring gear bolts there are
Monzaz: yes, I'm sorry. This thing is overhead in a garage and I could barely reach my arm up to take a photo down through the top of the old box while standing on some tires. The box is near disintegrated with age, so I was worried about dropping the posi on his car. I'll go back and see if I can get some more photos. Really appreciate your reply and am anxious to see what your verdict is.
I have swapped a rear from a '71 Catalina (maybe it was a '73 I don't remember) into a '75 Electra, no issues. The Catalina was 3.08 posi. I wanted the positraction more for pulling up slippery boat launch ramps. I "thought" the 3.08 ratio would be a bonus over the 2.56, but it felt nearly the same as far as towing peformance
