I want to change my diff lube this weekend. I bought 2 bottles of the Mobil 1 Synthetic 75w-90 and a bottle of Trans-X posi-trac limited slip gear oil additive. Just wondering how much Oil I will put in with the 7oz posi additive?

 

Add the additive first, then the oil.... Fill until it runs out the hole on the side.. usually 2 / 2.5 quarts....

 

Put the car on jackstands so it is level. Fill it till the fluid starts coming out of the fill hole. My manual says 3.5 pts.
About the posi additive, I read of people having issues when not using the GM additive, such as the rear making noises when turning.
Here's a link for changing fluids.

http://www.bfranker.badz28.com/fbody/lubeoil.htm

 

I just changed mine a couple of days ago, used up 2.5q of 75w-90 and some lsd/posi additive which i bought from autozone and my diff dosen't make any sounds while driving straight or turning.

 

You have a Zexel-Torsen differential, which uses worm gears to transfer torque. The additive is for differentials that use friction material to equalize or transfer loads. For instance an Auburn uses cone clutches, an Eaton disc clutches.
As far as volume goes, I just repeated what was in my owners manual. What does yours say?
My '98 S-10 has a limited slip, but the manual calls for no additive. I assume it has a Zexel.
I have used synthetic fluid in my Auburn with no additive and had no issues. I have read on this board where people have. That's what I was conveying.

 

My owners manual told me to use the GM lsd additive, but now your saying i don't need to use it i have no problem with that if its true since a bottle of that stuff is 15 bucks.

 

I can't answer that. I thought all LS1's had the Zexel, maybe I'm wrong. I'll see if I can find some info on it. The additive at a dealer is only $8, or was a couple of years ago.

 

On the Torsen site, they say GM issued a bulletin to use the additive. Here's a link.

http://www.torsen.com/general/genera...difier%20added