If you use a synthetic gear oil that has a friction modifier, do you still need to add a can of limitied slip additive?

 

Due to the massive responses, I looked into it a little. The answer is not clear cut for I had read only a few sites that said you do not need to add it and others do not mention it at all. I guess it is time to call the distributors and vendors.

 

What brand did you find that already has the friction modifier in it?
I wondered the same thing when I did mine. They had about 5 different brands at Napa when I bought mine and I remember seeing one that had it in it but it was synthetic also and I was told to use non-synthetic so I took a pass.

 

I do not recall exactly at this moment. But, I think it was a RedLine product. It will say that it has a friction modifier. When I was talking to Jegs about the differential cover, I asked the Tech aboutit. He stated to add it. However, I will probably call Royal Purple or Redline. I also plan on calling Eaton and Auburn and see what their recommendations are.

 

I recall a Horsepower TV episode where they changed all the fluids in a car to Royal Purple to see the difference in horsepower (by the way it was 7hp more). They said the synthetic gear oil was for a limited-slip diff. I've changed mine so either you don't need an extra additive or they have told a lot of people to ruin their locker.

 

I know from personal experience that the Amsoil Severe Gear works just fine as it is. They do have an additive you can add if you want, it does not hurt anything if you do and do not need it.

 

Actually I copied and pasted a note from the Amsoil site. There must be something about coding on this site and quotation marks. Anyway, on the Amsoil site, when talking about their LSD additive, it states that it is not needed if you were using their synthetic because it already had a friction modifier. However, if a chatter developed, you could add the additive on top of the synthetic without problems.

So this leads me to believe that you can go either with or without as long as the synthetic contains a modifier and the LSD does not beginning chattering. So for the price of the additive, it is probably worth adding it in advance and not worrying about it.

 

I used redline in mine and it doesn't need the friction modifier. Not that you need to worrk about it, the g80 is an auto-locker not a LSD.