I have 1970 Chevelle with a 12 bolt, bought it almost a year ago as a basket case. Been slowly doing body work, but last weekend I decided to try to determine what I had in the rear end. I have heard that if you jack up the car in the rear and spin one of the wheels, the other wheel spinning the opposite direction means you DON'T have posi, I have also heard that if you spin one wheel, and the opposite wheel doesn't spin, that you do have posi. But what does it mean when you spin the wheel, and the opposite wheel spins the same direction? Is something broken? If anyone here can make sense of all of this, I would appreciate it!

Thanks
Ryan

You may have a spool in it. Pull the cover and have a look. It'll give you the opportunity to count teeth to check the ratio. In a 40 year-old car, you don't know what you have until you put your eyes on it.

Both spin the same direction should indicate a posi.

Best thing is to pull the cover and see if it has clutches and such in there.

Thanks for the quick response guys, now to show my "lack of rear end knowledge" is there something that sticks out when I pull the rear cover that will give me an "ah-ha" moment and I will know what a spool, or clutches are? I have zero rear end mechanical knowledge, except on how to pull the rear cover off.

http://thumb7.webshots.net/s/thumb3/1/4/61/55410461hkgqKB_th.jpg (http://rides.webshots.com/photo/1055410461041712107hkgqKB)
If the differential has 4 springs and 2 plates in it like this then it's an Eaton Posi. I doubt that you have a spool. If both wheels turn the same direction then it usually means that you have a limtied slip differential (posi). If they turn in opposite directions then it usually means that you have a standard differetnial, or a posi with worn out slutches.

If it's in park, the other wheel will spin opposite regardless once you've overcome the posi pre-load, which doesn't "feel" like a lot when turing the tire by hand. Put it in neutral and turn the wheel slowly (so that it doesn't overcome pre-load) and a posi should turn both the same way.

Thanks for the pic Freddie. I am going to attempt to take the cover off tonight, and post pictures here tomorrow. Since I don't know what I am looking at, and you guys do, then that would probably be the best bang for the buck! Thanks again! Pics tomorrow.

Here are the pics of the rear end with the cover on and off. Please let me know if this is posi, has a spool, is an eaton, etc and any other info would be appreciated. Thanks!

http://i669.photobucket.com/albums/vv53/RynoH/th_chevelle2.jpg (http://s669.photobucket.com/albums/vv53/RynoH/?action=view&current=chevelle2.jpg)

http://i669.photobucket.com/albums/vv53/RynoH/th_chevellerear1.jpg (http://s669.photobucket.com/albums/vv53/RynoH/?action=view&current=chevellerear1.jpg)

http://i669.photobucket.com/albums/vv53/RynoH/th_chevellerear2.jpg (http://s669.photobucket.com/albums/vv53/RynoH/?action=view&current=chevellerear2.jpg)

http://i669.photobucket.com/albums/vv53/RynoH/th_chevellerear3.jpg (http://s669.photobucket.com/albums/vv53/RynoH/?action=view&current=chevellerear3.jpg)

Yeah ,appears to be a posi -might be Auburn,hard to tell.
What's the number on the carrier?

Thanks for the quick response Mike!

Where would the number on the carrier be?

That's an Eaton Posi. The casting number on it will be EDB30140. It's next to the bearing on the side opposite of the ring gear.

To sum it all up : You scored dude! Gratz!