# gear oil?



## AlanSr (Jan 4, 2008)

I want to change my gear oil and want to usr royal purple.
Which weight should I use?


----------



## GTO JUDGE (May 14, 2005)

SAE 75W-140 GL-5 Synthetic Gear
Oil (GM Part No. 89021809). With a
complete drain and refill add 1 oz.
(25 ml) of Limited-Slip Differential
Friction Modifier 7098
(GM Part No. 89021958).

I believe the Royal Purple has the F.M. included in it.


----------



## GM4life (Mar 18, 2007)

Judge is correct. If you use Royal Purple it has limited slip additive in it. I've used RP before for my diff.


----------



## AlanSr (Jan 4, 2008)

WOW!
This stuff is amazing!!!
My car drives silky smooth now. Next payday all my fluids are going purple


----------



## WanaGTO (Sep 7, 2008)

What did you put it in that you are saying your car is silky smooth?


----------



## AlanSr (Jan 4, 2008)

I used royal purple 75-140.
It already f.m. In it.
I'm not sure how to explain it but it made a world of difference.
I'm going to use it in my full size van also.


----------



## Poncho Dan (Jun 30, 2009)

How often are we supposed to change the diff fluid? I don't see it anywhere in the manual.


----------



## GTO JUDGE (May 14, 2005)

Personally I would change it out about 75K or so. Maybe sooner if you are hearing noises. Judging by the oils Dana used and the issues associated with rearend whine and break down of the oils, it maybe wise to do this for the first time about 25K or so and replace it with a good quality synthetic oil with F.M. You should then be good to go for a good 75K or so. I am basing 75K on other vehicles I had had that called for the change out about then and those were NOT synthetics.


----------



## B-ville Goat (Oct 5, 2008)

If you have a 6 speed car, definitely try the Synchro Max in it. Makes the trans a whole lot smoother!


----------



## jpalamar (Jul 22, 2008)

Doing mine this weekend as well.


----------

