Rustbucket2

I see a lot about O type rear ends! From what I read here a O ( open) type 12 bolt rear in cutlass, is not a posi ! So is this a 12 bolt ,one wheel peel ? ( only pass side turns)? all I ever knew was all 12 bolts are posi! Why would Olds make a 12 bolt , that's not posi? Just trying to get more knowledge into my brain. thanks

1970greensupreme

Oh boy, this poor soul is gonna hear it. In a nutshell, 12 bolt means 12 bolts that secure the ring gear to the carrier. It so happens that Chevy 12 bolts have 12 bolts that secure the outer cover. So do "O" type rear diffs, meaning Oldsmobile. Olds rears, although having 12 bolts on the outer cover only have 10 bolts that secure the ring gear to the carrier. There is a lot more involved also but all rears are available as open or limited slip regardless of how many bolts, who makes them etc.

jensenracing77

lol...

greensupreme is correct. The O type is not the same thing as a "12 bolt" Chevy that you are thinking of. My rear end guy says that stock for stock, the O type is stronger than the Chevy rear but the O type has nearly no aftermarket parts available.

anthonyP

Even though the Oldsmobile 12-bolt has only 10 bolts holding the ring gear, are they not larger and stronger?

joe_padavano

There are different components in the rear that can be the weak link. The Type O axle uses an 8.5" ring gear vs. the 8.875" ring gear in a Chevy 12-bolt. The larger ring gear diameter typically reduces loads on the individual gear teeth, making them less likely to fail for a given load. On the other hand, you are correct about the bolts. The ten bolts in the Type O ring gear are actually larger in diameter than the twelve bolts in the Chevy and are able to transfer a higher torque into the carrier. There are other differences in bearing size, axle shafts, etc.

oldsmobiledave

Who ever said that all 12 bolts are posi? That statement is 100% false.

BangScreech4-4-2

Besides, Olds never made a "Posi" at all. Their limited- slip was called "Anti-Spin".

VC455

The O designation is for Oldsmobile and, as has been pointed out, can be either anti-spin or open.

jensenracing77

Don't think anyone used the word Posi for the name. Limited slip and anti spin are the same thing just different name by different manufacturers. I believe posi is just a generic term for all of them? I could be wrong, did someone use Positrack as a name?

joe_padavano

Positraction is the Chevy marketing name for a limited slip differential. It should surprise no one that in our Chevy-centric world they are all "posi" units (just like all factory sport wheels are "rally wheels").

Here's an interesting list from Wikipedia of the various factory marketing names.


In the 1950s and 1960s many manufacturers began to apply brand names to their LSD units. Packard pioneered the LSD under the brand name "Twin Traction" in 1956, becoming one of the first manufacturers. Other factory names for LSDs include:

• Alfa Romeo: Q4, Q2
• Audi: Quattro, Quattro with Sport Differential (rear axle)
• American Motors: Twin-Grip
• Buick: Positive Traction. Gran Sport models used the term "Limited-slip (differential)"
• Cadillac: Controlled
• Chevrolet/GMC: Positraction
• Chrysler: Sure Grip
• Dana Holding Corporation:Trak-Lok or Powr-Lok
• Ferrari: E-Diff
• Fiat, Lancia: Viscodrive
• Ford: Equa-Lock and Traction-Lok
• Hyundai: HTRAC
• International: Trak-Lok (clutches only) or Power-Lok (clutch and ramping engagement process)
• Jeep: Trac-Lok (clutch-type mechanical), Tru-Lok (gear-type mechanical), and Vari-Lok (gerotor pump), Power Lok
• Lincoln: Directed Power
• Maserati: Equ-Tor
• Oldsmobile: Anti-Spin
• Pontiac: Safe-T-Track
• Porsche: PSD (electro-hydraulic mechanical), Porsche Torque Vectoring/Plus (PTV/Plus, combined electro-hydraulic mechanical and brake-based type; rear axle only)
• Saab: Saab XWD eLSD
• Studebaker-Packard Corporation: Twin Traction
• Toyota: LSD
• TVR: Hydratrak
• Yukon Gear & Axle: Duragrip
• Mercedes: ASD, AMG Rear-Axle Differential Lock (active differential on select FR-based AMG/S models; pure mechanical variant also present on select non-S AMG models)

droptopron

Interesting list

Koda

My father actually commented, while discussing his Corvette, that it was a posi, or limited slip or whatever it's called, so I replied that it was all the above and he was right.

dream66

.......

monzaz

Limited Slip Differential ...It is what all the new GEN calls two wheel peel.

LSD (like the drug yes)

It is always the easiest of terms that make the coin terms...It is just people being lazy AGAIN....

Back in the dauy that was how you identified what car people drove by the terms they used for performance...

If you said power lock or sure grip you were Mopar guy,
Safety track was Pontiac...Twin grip was AMC guy.... This is what we refer back to the GOOD OLD DAYS.... lol

Jim
J D

monzaz

This is true, LIMITED SLIP DIFF was an option like anything else on the car.

MOST cars did not come with this LSD option...most were just plain old open non POSI / LSD rears.

NO matter if it was a Chevy Olds Pontiac caddy Buick Mopar ford etc....Most all cars were open planetary spider system ONE WHEEL PEEL.

Most older cars price tag for this option was in the 20-40 dollar cost...LOL...
Another reason LSD option was low on the check list is because it was NOISY option. steel clutches and the maintenance of oil changes to keep it quiet were a pain... cause the dealership more headaches....

Jim
J D

monzaz

Limited Slip Differential ...It is what all the new GEN calls two wheel peel.

LSD (like the drug yes)

It is always the easiest of terms that make the coin terms...It is just people being lazy AGAIN....

Back in the dauy that was how you identified what car people drove by the terms they used for performance...

If you said power lock or sure grip you were Mopar guy,
Safety track was Pontiac...Twin grip was AMC guy.... This is what we refer back to the GOOD OLD DAYS.... lol

Jim
J D