Posi Diff Gear Oil ?????
 

I did try searching misc words and didnt find old threads
discussing what Brand/Viscosity Gear Oil is popular.

GURU who rebuilt my 10 Bolt with new Everything (Used OE Gears)
suggested Kendall 85-140 that contains posi additive.
I searched Kendall web site and cant even find it..........

Do I have to buy the separate GM additive ???

Valvoline 85-140 with GM additive is what my diff guy uses.

Dump the Valvoline in it -- if it chatters ... add the GM posi additive. Find a parking lot and drive slowly it in a figure eight a number of times. TAZ

Which differential was used in the rebuild? Was it a Eaton Posi, Auburn, traction Lock or something else? Some differentials need more additive than others. The Eaton Posi and traction Lock usually only need one bottle of the GM additive. The Auburn usually needs two bottles.

I don't use 140 oil in a car. The 80W90 or 75W90 is plenty for a car. If you are towing with a truck then the 140 would be fine. If you can find Torco TGO or TRO oil then use it. I've been using Lucas in a lot of rear ends lately, and Mobile 1 if I want a synthetic.

Freddie, I just want to confirm that you are not using the synthetic gear oil.
Lucas 80-90 is petroleum gear oil, not synthetic.....

Should I ONLY use the GM additive ?? Is this same as AC/Delco branded posi additive ??

GM posi additive is 88900330 ... TAZ

Yup.

http://www.ebay.com/itm/Ford-Motorcr....c100337.m3725

FORD additive.....................

I've used many different oils with the Eaton Posi, with steel and carbon fiber clutch discs, and didn't have any problems with any of them. I used Amsoil synthetic in probably about 100 of them and it worked great with no additive. Amsoil has changed their oil a few times since then, so I don't know how it works now. I've used about all of the other brands in synthetic and petroleum base and they have all worked fine with the correct additive. I found that the GM and Ford additive work best. I'm giving Lucas a try now and so far so good.

I know that this doesn't apply to you, but Torco oil was the only one that would work in the '06 GTO rear end that I rebuilt. Amsoil only worked for a little while and then it started making a lot of noise. The Torco oil made it quiet again. I would use Torco in any cone type differential, such as the Borg Warner and Auburn.

Thanks Freddie for all your many years of experience