After trying 80-90 gear weight oil (petroleum based) , then 85-140 (petroleum based), then adding Lucas Heavy Duty Oil Stabilizer and now back to the 80-90 petroleum based gear oil, the 80-90 petroleum based gear oil seems to be the quitest in my Moser 12 Bolt with and Eaton Posi and 3:73 gears.

Question, the technician who added Valvoline High Performance gear oil (80-90 petroleum based) told me that I did not need to add any limited slip additive because the Valvoline High Performance gear oil already had the limited slip in the oil. The label on the large drum the gear oil was in read "meets all fill requirements for limited slip differentials."

Has anyone used gear oil with the limited slip additive already in the oil. I believe Quaker State sells gear with the limited slip additive.

The question then is, should I add a bottle of the GM limited slip additive?

Thanks!

 

I'd like to know more about this too, gonna change the rear end fluid soon.

 

Cwynn, just go to a reputable shop and have the fluid drained and have them inspect your gears and posi for any kind of wear problems. I would stick with the petroleum based (i.e., non-synthetic oil) oil as that is the oil recommended by GM. I have a Camaro Shop Manual and the recomended gear oil is SAE 80W-90 GL-5. Important that the gear oil used is graded at GL-5.

Note: I believe GM recommends chainging the gear oil every 25,000 miles. Just check your maintenance schedule.

Cheers!

 

What does Moser recommend?
It's gotta be expensive if you are having a shop do all of these drains/refills. If you are worried about it, get a bottle of GM additive and put it in yourself. It can't hurt anything.
Cwynn, if you have a 10 bolt, use the GM additive.