I'm about to change my M6 tranny and rearend fluid and was wondering what most people are using in their LS1s.

I'll probably go with Mobil 1 or Royal Purple in my 2000 SS. Do I still need the limited slip additive with synthetic? if not will it hurt if I still put it in?

 

I put Red Line 75w90 in the rear end. It has additive in it already so no need to put any in. For the tranny, I put in Red Line D4 ATF, yes you put ATF fluid in a manual...dont ask why

 

i was told if it says for limitied slip then you don't need the additive, with that said i'm almost at 5k miles after my change and no problems

 

Any non-synthetic oil. I know synthetics are the rage and they are extremely slippery and last a long time. At the race track synthetic fluid may be too slippery depending on the power level and certain brands of differentials do not like synthetic fluids (Auburn for example).

 

I use mobil 1 synthetic gear oil

Transmission I use dexron III

 

and you didn't put the additve in, right?

 

gm synthetics

 

correct, never noticed a difference between that and the old fluid anyway

 

What would happen if I used Mobil 1 and the limited slip additive? Would that help, hurt, or not make a difference?

 

The posi additive is for clutch type posi-traction units. 99-02 have a Torsen unit stock which doesn't have clutches so, no additive necessary. Now some SSs have different posis from SLP so, know what you have.
And from my experiences with trying synthetic in the T56. Don't.

 

Why not? So Mobil 1 or Royal Purple dexron III is no good for the T-56?

 

Anyone else got any advice for me? I should probably post this in the LT1 section too.

 

If you still have warranty I'd just put dexron III in.

 

What's everyone's opinion on the GM Synchromesh? Better than Dexron III? Gonna change mine soon too.