ARE all 8.5 posis the same

[Footjoy]

I was looking on ebay and saw a couple 8.5 posi out of suburbans do they fit a 1974 nova 8.5 rearend and some body said early chevelles are 30 spline.

Thanks

[GinoRin]

There's a few things you need to look at when making that decision:

1. How many splines are the axles you're using
2. Carrier bearing size
3. What ring and pinion gear ratio you are running. for instance, if you're running a 3.42 gear, you need a 3 series carrier. a 4.11 gear would need a 4 series carrier, and so on.

As a side note, I have blown up three different auburn pro series posi units, they seem to suck pretty bad. I have had REALLY good luck with the stock GM units and also the Eaton posi units.

Hope this helps!

[big gear head]

The trucks used the Governor Lock, which is fine for a stock truck, but not for a high performance car. There are too many small, weak parts in these. The '71 to '81 Camaros and Firebirds used the Traction Lock, which was pretty good, but getting hard to find. There is a new Eaton for the 8.5, which is very good. The Auburn is junk, don't mess with it. It was used in the SS Impala and some of the later car rearends.

The 8.5 has a 2 series and a 3 series differential case. The 2 series was used for 2.56 and 2.43 gears. The 3 series was used for everything else. Be sure that you get the right one for the gear ratio that you are using. There are also 28 and 30 spline axles, so be sure that you get that right too. As for the bearing size, if you get the wrong one that can be fixed with special bearings.

[Bandit]

There's a few things you need to look at when making that decision:

1. How many splines are the axles you're using
2. Carrier bearing size
3. What ring and pinion gear ratio you are running. for instance, if you're running a 3.42 gear, you need a 3 series carrier. a 4.11 gear would need a 4 series carrier, and so on.

As a side note, I have blown up three different auburn pro series posi units, they seem to suck pretty bad. I have had REALLY good luck with the stock GM units and also the Eaton posi units.

Hope this helps!

I highlighted #2 on Gino's list because not knowing this cost me $200...which was the going rate for a specialist I brought in from out of town to setup my gears. Turns out my install kit from drivetrain.com contained the wrong size bearings for my new Eaton carrier. They were the ones that fit my old diff (also an Eaton). (Again, I am in Europe and could not just go down to the local Napa for the bearings I needed. So we had to re-install the old diff and I had to try again another day. Drivetrain.com was good about sending me the correct bearings for free, but I was not happy about it to say the least!

As far as a diff, I like the Eaton clutch-type posis, they seem really tough in my experience...I have had 3, and I haven't broke any of mine yet...

[big gear head]

In '98 GM went with the larger 12 bolt differential bearings in the 8.5 10 bolt. All of the new Eaton units for the 8.5 have the same size bearing journal as the 12 bolt, so a special bearing is needed. The same bearings can be used to adapt the '98 and later differential to the earlier housings.