Toby, I've recently arrived on a part that desperately needs aftermarket support...
long story short, for a couple of years now the posi in my 8.5 10bolt has been getting slippy. Last summer I started doing to research to rebuild it during this coming summer. The whole unit is fine, it's just the clutches that need replacing.
the OEMs use a Eaton posi unit with an S-Spring clutch system. The new Eaton units use a coil spring & plate system. The components are not interchangeable.
after a few months of researching and asking questions, I discovered that GM discontinued their reproduction of these clutch packs. I suppose many aftermarket suppliers bought out the remaining stock, but have all run out. After a couple months of calling around, I've come to a dead end...
All other parts for this OEM Eaton unit are available, spider gears, thrust washers, pins, S-spring, etc... Just the clutch packs are missing.
they are very similar to the new style, but not the same.
the old style use "Square Ears
the new style use "Round Ears"
I've asked around to a few dealers. Suppliers like Randy at ringpinion.com and Nitro-Gear.com did manufacture these for a short while after they were discontinued from GM, so this tells me these are possible to make.I know GbodyParts.com carries the S-spring, the pins, and other components for these Eatons, but they have also run out of stock of these clutch packs.
As these 8.5s are so popular, so strong, I imagine there is a huge need for service parts for these units. And we are at a dead end with the clutch pack.