Royal Purple gear oil with addative included?

[TexasSpeed]

I'm looking to replace the diff fluid on a '03 Mach 1 8.8 this weekend. I had planned on buying the 75W140 and then the 4 oz of friction modifier. At the auto parts store, I noticed Royal Purple 75W140 that states it already has the friction additive included and no additional modifier is needed. Has anyone run this and do you really not need to buy any modifier to add??

Thanks,
Todd

 

[b_dike]

That's correct, rp includes the friction modifier in their formula. Using too much can actually be a bad thing. So don't add any if you buy rp. I personally run rp 75w90 with good results.

 

[Roots-type]

Correct. No need for additional friction modifier. I run solid lca's and the 75w140 royal purple will reduce the gear whine that can be heard when you switch to a less nvh friendly control arm when compared to the 90. The 140 also protects better, just slightly less efficient than the 90.

 

[TexasSpeed]

Thanks for the details.

 

[UnleashedBeast]

If you use any gear lube, and get chatter from the clutch packs, add 2 ounces of friction modifier. If it still chatters, add 2 more ounces. Trick is to use the minimum amount to prevent chatter.