1. What is a Posi, and what does it do.
2. Did all camaro's come with them.
3. is a 12bolt better than a 9in ford?
4. What chevy's came with a 12bolt
5. " " any come with a posi?
Thanx in advance J. Howard.


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red camaro with v6 that still kicks but

 

1. A "posi" is basically a limited-slip differential. On an "open" rear, or non-posi rear, both rear wheels are almost independant of each other. You could hold one wheel while spinning the other. This is because in a turn, the outboard wheel turns faster than the inboard wheel. A posi basically tries to keep both wheels spnning at the same rate. Posi units allow some slippage because of the turning desribed above. A posi transfers power to both wheels while an open rear tends to transfer power to just one wheel. That's why open-rear cars usually only spin one wheel in a burnout while a posi equipped car will spin both.
2. No. My '92 RS did not come with a posi rear. Most higher performance Camaros (Z28's, IROC's, etc) came with posi rears while most base model Camaros came with open-rears. That seems to be the case barring a few exceptions from what I've seen.
3. I have no idea.
4. Again, I have no idea.
5. And yet again, I have no idea.

 

9in fords are suppsed to be the toughest around..hey..looks like Ford finally got something right!

I prefer not to run posi on the street, actually posi + stupid driving is what made me wreck. It's safer to accellerate through turns with an open rear. Trust me, I learned the hard way

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'92 Formula
305 TPI 5speed
1LE package
Mods: SLP headers,SLP catback,SLP air foil,ported plenum,Crane AFPR (42psi),MSD6AL,homemade cold air,K&Ns,3:73s,JET fan switch, Macewen white face gauges...ZZ9 cam (i still have to install it )

 

1) Posi (limited slip) limits the difference in rotating speed between the rear wheels
2) some/most high performance came with them, i believe they were optional on all models as a special order
3) both 12 bolts and 9" are good, the 9" is more modular and easier to modify, hence its popularity. If you look under a 57 chevy, you will see that GM used the same style rear back then, but changed in the late 50's (help me with the year?)
4)No thirdgens were ever made with a 12 bolt. they cam in trucks, 1st and 2nd gens (some) and chevelles (some). Some had Posi. THe 12 bolts are very popular for racing, so all the parts to make them race-worthy are available at a reasonable $$$
5) i will never own a rear wheel drive car or truck without a posi

 

12-bolts also came in full-size Chevys (Impalas) and many big-block Novas. Both open and posi units were made.

The non-modular carrier 10-bolts (vs. the modular '57 rears as mentioned above) started in 1963.

Almost every style differential has had a posi model.

Both 12-bolts and 9" rears are very strong. The only advantage I've ever heard performance-wise is that the 12-bolts are slightly more efficient. But, 9"-ers are much more popular now for the reasons stated by merf.

To get anything other than a factory-style rear with the torque arm provision into a thirdgen is going to require a custom rear, meaning lots of $$$'s. To need anything stronger than what you can make a factory-style rear will require a lot of engine.

I have compiled this information by owning (or working on those owned by relatives), over the years: '57 Chevy (4 total), ('60 Impala - Grandfather), '62 Chevy - wife's car when we got married, ('63 & '64 Impalas - other Grandfather & his brother) '66 Impala (1 ea self & brother - his was an SS), ('67 Caprice - brother), ('68 Bel Air - Grandfather traded in the '60), ('69 Impala - Dad, took my 1st driver's license test in that car), '70 Impala, '73 Nova, '79 Caprice, '82 Camaro; and getting parts for and modifying the above (such as the '71 Nova 10-bolt in the '57 right now). The '66 that donated the 396 in the '57 is the only one that had a 12-bolt - all others were 10-bolts of one sort or another. The '62 and '79 are the only ones that had posi. All were V-8 cars. I'll not list Vegas, Ramblers and the like.

How's that for a bunch of info you didn't ask for?

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82 Berlinetta, orig V-6 car. Rescued w/86 LG4/TH700R with all harnesses, sensors, ECM, etc. 2.73 unlimited slip. Cat-back from '91 GTA, Accel HEI SuperCoil. AMSOIL syn lubes bumper-to-bumper. Daily driver, work-in-progress (LB9 w/ZZ3 cam, exhaust, paint, etc.).
57 Bel Air, my 1st car. Currently 396 .030 over, Weiand Action+, Edelbrock 1901 Q-Jet, Jacobs Omnipack, 1-3/4" headers, TH400 w/TCI Sat Night Special conv & shift kit, 3.08 10-bolt, AMSOIL syn lubes bumper-to-bumper. Best 15.1 @ 5800' Bandimere. Daily driver while Camaro was being put together.