I opened up the cover on my differential and this looks like nothing in the factory shop manual that i have.

 

Looks like possibly a Detroit Tru Trac or a Gov Lock.

 

10 BOLT 8.5 REAR
IT IS SOME FORM OF A TORSEN POSI (TRUE TRAC WORM GEAR POSI... )

I can not tell if that is old school first design torsen posi or New unit ... to me it looks old school first design torsen posi ... It is a cool find for sure. I would love to see if there are any markings or casting numbers date codes? More pictures? What kind of bolts hold the unit together? Hex head Allan head???
Oh by the way the pattern is too deep on that set-up
You should take some shim out from under the pinion and reset backlash again. Needs to move up and out for the root of the tooth .

Jim
JD Race

 

I will take some more pictures this week end. How can I determine what the gear ratio is if nothing is stamped ?
I

 

If not stamped, then counting the number of teeth on the ring gear and pinion is one way.

 

To finish up for Fun71. Number of ring gear teeth divided by number of pinion teeth.

 

example
12 pinion into 41 ring is 3.41666666 Round up 5 or higher to the second decimal is 3.42
11 pinion into 41 ring is 3.7272727 Round up 5 or higher to the second decimal is 3.73

Hope this helps.

There are NO markings at all on the ring or the pinion head / crown? Jim

 

Remember this is a torsen / true trac type posi and you can not do the spin test like a traditional clutch or cone friction posi. Which has both wheels locked under no load.