Rear End Fluid

[gnonyx]

Hi All,
Would it hurt if replacing the rear end fluid with Mobil 1  75W-90 Synthetic Gear Lube - 1 Quart,
plus adding GM Fluid 88900330 Limited Slip Axle Lubricant Additive - 4 oz., and of coarse including a new Fel-Pro gasket
Thanks

[Steve Wood]

There seems to be a lot of mixed opinions on the subject.  Some say no problems.  Some say do NOT add the additive.  Others say only use the additive if it chatters going around corners.  A few say Eaton says do not use it because it is too slick and the clutches need friction...and you can google just like me and get confused too.

Personally, I don't see the need for it.  Any performance gain is probably more theoretical than anyone could actually measure.  I don't believe the clutches were made with it in mind back in the day.  I would stick to conventional non synthetic.

Before the day is over you are bound to see people that disagree strongly and claim to be a second faster using it.  LOL

[xracerx13]

On my stock rear end after adding a drain plug to the stock cover with new gasket obviously, i used redline synthetic 75W90 gear oil with GM posi differential additive. At first i didn't think it needed the gm posi fluid.  but I had to add it cause it was making noise around corners like Steve said.

[ULYCYC]

I always had best results with GM limited slip gear oil with 1 bottle of gm additive. This is for stock diff and gears.  With a Eaton unit and after market gears Lakewood limited slip racing fluid (yellow bottle) with 1 bottle of gm additive. I never had issues or chatter,clunking with either.

[gnonyx]

There seems to be a lot of mixed opinions on the subject.  Some say no problems.  Some say do NOT add the additive.  Others say only use the additive if it chatters going around corners.  A few say Eaton says do not use it because it is too slick and the clutches need friction...and you can google just like me and get confused too.

Personally, I don't see the need for it.  Any performance gain is probably more theoretical than anyone could actually measure.  I don't believe the clutches were made with it in mind back in the day.  I would stick to conventional non synthetic.

Before the day is over you are bound to see people that disagree strongly and claim to be a second faster using it.  LOL

You know I have always used conventional oil and not synthetic oil, and this was one of those questions I needed to know if anyone was converting to synthetic type.
I'll stick to the old school ways since I never had a problem
Thanks

[1KWIKSIX]

Instructions from the manufacturer for My Auburn limited slip differential warned not to use synthetic oil in their rear end. Just Dino oil and limited slip additive .

[gnonyx]

Instructions from the manufacturer for My Auburn limited slip differential warned not to use synthetic oil in their rear end. Just Dino oil and limited slip additive .

Thanks for the info and yes you're right I'm not going to use synthetic oil for the rear end  and not even motor oil, as I only used conventional oil.