GM differentials

[Ghoste]

Were they division proprietary?  That is to say, is an Olds 10 bolt the same as a Chevrolet one?

[c00nhunterjoe]

No, they are different. I know this because a friend is going through this dilema. He has a 70 chevelle that he just bought a "chevy 12 bolt" for. After a lot of head scratching trying to figure out why the new wheel bearing and seals didn't fit we found out its a buick(I believe). The axles are not c cliped like a chevy rear, its more lik a mopar 8 3\4 with rotary slack adjusters. Other then the internals it bolted right onto his car

[Ghoste]

Do GM guys have differing opinions as to which are better?

[440]

12 bolt in the Chevy world is like an 8 3/4 in the Mopar world. 10 bolt was standard.

[Ghoste]

But is the Chev considered stronger than the Olds for example.

[Cooter]

There were so many different GM rears. You have the "truck" set ups, then the older "car" set ups. Most refer to the "10 bolts" as one of two different offerings.

1. Old style 10 bolt
2. New style, or "Corperate" 10 bolt.(Think 1987 Monte Carlo SS, S-10 pick ups, Most full size trucks, etc.) Most had that stupid "Centi-lock" crap or whatever...
Basically, it was a little Centrifugal weighted piece that flew out when one wheel began to spin and supposedly "locked" the rear. Can you imagine how well this worked on ice? Yep, blown up rears in late model trucks usually can be attributed to this..

Both had 10 bolt cover bolts, but were very different. The 12 Bolt everybody seems to think was the strongest of the GM Musclecar line-up is IMO, like their Muncie "Rock crusher" trans. Nothing strong about an aluminum transmission. Only that it sounded like one was "Grinding rocks" inside when cruising down the road.
I've personally sold more Chrysler A833 4-speeds to "Chevy" guys than Mopar guys for this very reason. Yet, a "Rock Crusher" will bring $1000-up, and a stronger? Chrysler will "only" bring around $500.00....Sad..

Same thing with their rearends. A "Car" 12 bolt I've sold for $1200.00 with Posi. Yet an 8 3/4, "489" Sure Grip, 3.55 Gear rear won't fetch over $700.00?....
Again, sad.

454's VS 440's? Forget it...I've sold 1975 Model, Low comp, Cast crank, Oval port Headed, "Dumptruck" 454's for over $1000.00 for a core. Yet, a much harder to find STEEL crank 440 with "good" heads won't sell @$1000.00?


As for GM guys on which is better? Most will say "Put a 9" in it"...Or a Dana 60.

[440]

The axles were different in the trucks and some of the large cars. 5 on 4 3/4" was most commonly used and trucks and some large cars got a bigger 5 on 5" pattern.

[c00nhunterjoe]

The rear that ended up in my buddys chevelle has 31 spline axles, and has bolt in axles. It is stronger then the chevy 12 bolt.

[surmanajaja]

chevs have 8,2 inch and 8,5 inch 10-bolts, and 12-bolts. 8,5 can survive 300hp, 12-bolt 450-500 but theyre all mostly crap, thats why all nascar chevs and smokey yunick trans am camaros alll had ford 9 inchers.  old 50s oldsmobile and buick 10 bolts are better than later chevs.

anyway mopar 8,75 and ford 9 is always stronger than any factory gm.

[Ghoste]

Did the Olds and Buick ones remain the same through the 60's?

[surmanajaja]

GM began building 10-bolt, Salisbury-style integral rearend housings in 1964 (as opposed to the drop-out style used from '55-'64) for Chevelles and later Camaros and Novas. These were 8.2-inch ring-gear-diameter housings. The Buick-Olds-Pontiac (BOP) stuff also used 8.2-inch-diameter 10-bolt ring gears, but the internal parts, including the gearset, are not interchangeable with the Chevy-style axle. The 12-bolt Chevy rears were 8.875 inches in diameter. In these rearends, the number of bolts on the rear cover is the same as the bolts used to attach the ring gear to the differential.

From '68 to '70, Oldsmobile used an axlehousing with a 12-bolt rear cover, but internally, it employed an 8.5-inch-diameter ring gear with 10 attaching bolts. they're all 10-bolts. This is still an 8.5-inch-diameter carrier, so it is stronger than the 8.2-inch 10-bolts, but it is somewhat rare, as its internal parts are not the same as other "corporate" 8.5-inch housings used in later GM models. Richmond Gear does make 3.42, 3.90, and 4.10 gearsets for this Olds-only (not BOP) axle assembly, and according to Richmond's catalog, those gears will fit a 2.93 through 3.23 ratio differential. The basic rule of thumb is that a 2-series differential will only work with gear ratios in the 2 series, as in 2.56 or 2.78. The other ratio series follow a similar path. This is not a hard-and-fast rule, however. For example, one Buick/Pontiac 8.2-inch rearend differential will mount 2.87 through 3.31 gears, while another will accommodate 3.36 and deeper ratios well into the 4s. So you need to be careful here when matching a differential with a given ring-and-pinion. Just to make it more confusing, many aftermarket gear companies offer, for example, a 4.10 gear for a 12-bolt Chevy housing that will mount to a 4-series carrier as you might expect. But some companies also make a 4.10 gear that will mount on a 3.08 through 3.73 (3-series) differential by making the ring gear thicker.