My Buick has a 12 bolt rear--but my local Buick guru says it is an OLDS 10bolt it is stamped S7 ---I dont know the year it appears to be posi can someone ID the gear ratio?? Also are gears availble for this rear? Thanks Pete
The rear you sent a pic of is indeed a Type "O" Olds 10 bolt. While Olds guys love to mistakenly call it a 12 bolt, it's not. The only thing "12 bolt" about the type "O" Olds rear is number of bolts attaching the smooth rear cover (not the same bolt pattern as Chevy 12 bolt). Internally, the type "O" used a 10 bolt ring gear, 8.3-8.4"s in diam. Basically, the type "O" 10 bolt is the forerunner of the corporate 8.5 10 bolt. While strong, the type "O" does not have the added pinion support that the 8.5 has, so it cannot be be built as strong as a well prepped 8.5. The type "O" Olds rear also suffers from the lack of a wide variety of aftermarket parts, making it very expensive & nearly a moot point to build up single track core rears to desirable ratio posi rears. Further identification... With S7 stamped axle tube, the rear will be either '67, 68, or '69 3.23 AntiSpin (posi) application, but may even be '70 piece. The '67-69 application shows HD brakes, should use different backing plate & accept wider brake shoes, at least thats how a '68 S7 was that I bought missing one axle, & rebuilt in the late '90's & sold. If you unbolt & pull an axle, & the axle has external seal, outboard of the bearing, it is a '70 with tapered bearing axles. Unfortunately, there is not much good printed ID info on the '70 type "O"s. Certain '70 type "O" axles are hard to find, & they didn't even make it into the Hollander interchange. For aftermarket gears, there are/were Richmond 3.42's & 3.91's being made in a thicker variety to fit the mid ratio (3.08-3.23) carrier. They're not exactly cheap, but should still be avail from Tom's Differential, Randy's Ring & Pinion, or Supercars Unlimited. Got Posi? :3gears: Roger
Don't have a list of axle codes in front of me, but you can find that in 442.com. Olds 12 boltsa are really a 12 bolt cover with a 10 bolt ring gear, They were produced in 1967-1970. In 1971, Olds went to the corporate 10 bolt 8.5 design. My guess is your car was built in a BOP plant (not in Flint) so it could easily have a different rear end in it. They were interchangeable and the remote Assembly plants (non Michigan) substituted a lot of parts like that. Canadian 442's got Chevy 12 bolts put in them back then. If it's the original rear in your car, your car is a 1970 or earlier, and has 12 bolts on the axle cover, the only place i know that sells gears for that axle is Supercars Unlimited in Oregon. They can also help you identify that code, ask for Greg Rollins, the owner. Great guy. If your car is a 1971 or newer, has the original axle and a 10 bolt cover, it's the corporate design and gears are available about everywhere even if it's an Olds built version of it.
Thanks guys,my problem is the323 gear,combined with 28.1 inch tall rear tires and a 2:20 first gear make getting going a little tough.If I leave the gear and go down to a 26" tire I think I can almost end up without a gear change and get rolling a little easier plus 2 different size tires FRONT/REAR does not excite me from a driving/handling standpoint---would rather have 245x60x15 all around. Pete
Hey Pete, This is getting creepy! no only are our cars almost identical, mine has a 12 bolt olds in it too:eek2: Mine has a 3.90 gear, good for take off with the 2.20 first, but too much gear really. I have had mine in there for years and can attest to their durability, its taken some abuse:3gears:
Hi Adam --yeh that is weird---my 3:23 rear is good on the HWY --wondered why I was getting 14 MPG!!!! Seriously I think I might bring thr tires doen a couple sizes---dont like the assend riding up in the air---when I pick up my daugter at HS all the guys are jumping to get a look at this critter:laugh: Lovely 70 degree day here in SOCAL--screw that groundhog:blast: Pete
Pete, like Roger said, Richmond makes ring and pinion sets for that "O" axle. If yours is a 3.23 like Roger said, you're in luck, because that's the posi carrier Richmond's gears are made for. Otherwise you'd have to replace the carrier. ($$$$) Your choices are 3.42 (only a 6% change) or 3.90 (my favorite, unless you spend a lot of time on the highway). They might still offer a 4.10 set, too. I don't think you should go with smaller tires. I got worse traction with the 26" drag radials than with the 28". And frankly, the 26" is borderline for looking a little small in the wheelwell. 28" tires with 3.90 gears is a nice combo. If you're having troubles getting that thing rolling, don't forget carb- and timing-adjustments.
Thanks Brian dont see much use for 342 and 390 is way too much for going to shows/events here in SOCAL which are ususally 150 miles round trip.Actually it isn't that tough to get rolling cause the 455 LOW end torque is always there!! Gotta do something about the tires 225x70 front 275x60 rear makes my car handle like siht---but that's the way it came and it IS a Buick 4spd:3gears: I guess there is no 373? Pete
150 miles round-trip is really not bad with 3.90 gears, softened by the 28" tires. But that's a matter of personal taste. I agree, the gap in between 3.42 and 3.91 in the gear sets offered by Olds is too big. I sure wish they had offered a 3.55, 3.64, or 3.73 like some of the other GM divisions. Having said that, you could certainly look for such a rear from another A-body. Or switch to the '71 or later "corporate"-based axle -- then you'll have an infinite selection of gears. Olds still made it's own version of this rear end, with the axles retained by plates, not C-clips. I checked my factory documentation last night and found that Olds used the "S7" coded rear in '67 - '69. Like Roger said, it's a 3.23 limited-slip. It was installed in A-bodies with disc brakes up front. I don't know if the drum brakes on this rear were actually heavier-duty, or if maybe they just used a different piston size to balance better with the discs.
To me, a 3.90 gear is an awesome all-around gear. Not crazy RPM's cruising, while still having some *grunt* down low.
We put 50,000 miles on the Ramrod with the 3.91 gears in the first 5 summers we owned it. We always stored it 5 to 6 months per year during the winters. Longest trip was to New Orleans on our honeymoon. I also think it's a great gear even if the car was much quicker with the 4.56. Think that's much more critical with a high hp, high RPM small block, than a high torque big block.
..... of course, now you're taking advice from a couple of small-block Olds owners (Dave and Casey) who think that life doesn't begin until 7000 rpm ...... :laugh:
You guys have a case for your 3:90 gears but I will stick with what I have for awhile----again keeping up in LA traffic @ 70 I will be loafing with the 323 and again my low end torque gets me rolling,actaully once you get a feel with the clutch you can get a pretty good launch without losing the rear tires:3gears: +1 Pete
Wierder yet, Mine has a "O" differential in it also. It is a fremont car, 1969 GS California. It was a 3.23:1 posi but I took a set of 4:10:1 Richmonds and replaced them. Wow, I thought that someone had replaced the rear end at one time or another. Please keep the info coming...I like it.
