Identifying rear diff on 1980 C20. LSD or not?
 

My truck has a 14-bolt rear differential. I've removed the cover and drained the oil, and am about ready to button it all back up and refill with fresh oil. However, I can't figure out if this truck has an LSD or not, and therefore whether to add LSD additive into the oil.

Picture: https://imgur.com/VLqjWER

With the rear end jacked up, and transmission in neutral, when I spin one wheel, the other stays stationary. But if I put in gear and spin one wheel, the other spins the other way.

I'm inclined to think this means it does NOT have an LSD, but I'm getting so much conflicting information after searching extensively that I am not feeling very confident about this. Help?

Re: Identifying rear diff on 1980 C20. LSD or not?
 

The diff described and pictured is not an LSD...it is an open or standard diff...

:chevy::chevy::chevy:

Re: Identifying rear diff on 1980 C20. LSD or not?
 

4 windows and see spider gears = open

4 windows and see coil spring and block of steel = detroit locker ........... do NOT pull apart a detroit type unit unless you bolt the unit together inside or it will pop open good on you and might hurt .

3 pins on the center of case were the ring gear bolts and no windows = gov-loc posi unit .

3 pics in order as i typed above .

Re: Identifying rear diff on 1980 C20. LSD or not?
 

("3 pins on the center of case were the ring gear bolts and no windows = gov-loc posi unit .")
what k30 posted is what you have.....G80
it is not a open diff..it the GM version of a posi

Re: Identifying rear diff on 1980 C20. LSD or not?
 

forgot to add also . the strongest of the gov-loc posi units is the 14ff . i have run them stock to built 400 sbc engines with 38" tall super swamper mud tires and no problems .

Re: Identifying rear diff on 1980 C20. LSD or not?
 

This is helpful. Mine looks just like the first one. Four windows with small gears visible through them. So I assume this is an open diff and therefore I shouldn't put anything but gear oil into it.

Here's a better pic, you can see one of the windows and small gears: https://imgur.com/a/7u0Z6Hv

Re: Identifying rear diff on 1980 C20. LSD or not?
 

I think i see the windows now...so that changes my opinion...couldn't see them in the other pic...looks open

Re: Identifying rear diff on 1980 C20. LSD or not?
 

open diff or gov-lov both call for std gear oil in these axles .

and yes you have open diff .