I have a posi unit that I don't know the application for. It's a 12 bolt, 28 spline and it's NOT a 9 3/8. It has the 4 coil springs like the early 9 3/8, not the S shaped preload springs that began in '71. It looks just like a Chevy 12 bolt, but with 28 spline instead of 30. It takes an axle that is 1.2 OD at the spline. It measures about 1/2" smaller than my 9 3/8, so I assume it's 8 7/8 but I don't have any gears with it. Any idea what it fits?
I don't have anything other that the carrier. The Olds was a 12 bolt cover, with a 10 bolt gear if I remember correctly. I'm pretty confident that this carrier I have uses a c-clip style axle, because of some shiny spots on the cross pin. I'm guessing that the spider gears can be changed to a 12 bolt Chevy and it would become a 12 bolt Chevy with 30 splines. Any one else have any ideas on what this thing is from?
i may be wrong (not the first time),but i think the carrier may be from at 12bolt (8 7/8) truck axle. Ken.
12 bolt truck is 30 splines too. Anyone know if 12 bolts came in 76 and later full size GM cars (Electras and others)?
It is based off the 60's fullsize pntiac rears. it uses 8.875 ring gear BUT the ring gear bolts are left hand thread 7/16 20 count. The rear are all c-clip and came in 28 and 31 from 1971 to 1977 in caddys, pontiacs, buicks, and olds The cover will have a 10 bolt cover like the 8.2 mid size a-body cars but will be larger and have a bigger ring gear buldge in the cover. To an untrained eye they might look identical. THEY ARE NOT. So the rear will have a 10 bolt cover and 12 bolt carrier unit. This would be a good posi and stonger except they have no gear support in the aftermarket...So you screwwed again... ou: I think the best ratio you can get for it is 3.42 3.23 that is it. Most were installed in the early and mid seventies when gas was like it is now- CRUNCH! 2.41 2.73 2.28 are the most popular ratios. I have included some pics for you .
Thanks so much. You're the only one I've found that seems to know what it's from. Why isn't the 12 bolt Chevy ring/pinion interchangeable, other than the LH bolts? Now I need to figure out what to do with them-I have 2 of them. One of each offset.
Pinion is different too. Seems to be the same as a 8.5 10 bolt pinion... They are longer than the 12 bolt chevy pinion by almost 1". Just was never a performance rear when they installed them in the big cars. And being a seventies rear the ratios were not good for performance... NO overdrive trannies exsisted either. Crummy time for cars. Jim
Those came in 73-76 A body wagons. 77 referred to it as a 8 3/4. As well as some mid 70`s Grand Prix`s, Grand Am`s and Lemans eqiupped with ploice pursuit package. See em on ebay all the time incorrectly listed as 12 bolt chevys.
