Do I need a Friction Modifier in my differential

[4.6andSlicks]

I want to change the fluid and plan to use Amsoil Severe Gear 75W-90. Do I need to add anything?

 

[old_blue]

some gear oils (i believe royal purple) have the additive already in it. But yes you need to add it to a fluid change.

 

[98COBRA281]

oops i never put that in, maybe thats why my rearend whines

 

[spederman]

oops i never put that in, maybe thats why my rearend whines

I've forgotten to put in the friction modifier on an old 5.0 i used to have. They only thing it did was in a turn it would make a clunking sound from the rear end. I assume because it wasnt letting the LSD actually slip during turns. I never had a whining sound, i couldnt even tell that i forgot it on straight roads.

 

[98COBRA281]

it only happens at about 40 when the car is just kind of crusing

 

[spederman]

it only happens at about 40 when the car is just kind of crusing

I think thats just regular old gear whine from not being installed perfectly since it only does it at that speed. Thats what my 3.90's did in this car, right at 40mph it would whine. I dumped them for a set of 3.73 FRPP and no whine any more.

 

[98COBRA281]

if i remenber right mine are frpp

 

[DTNODYA]

If in doubt, just add it. But don't spill it on you because it smells terrible!

 

[98COBRA281]

i went to the auto parts today advanced auto, and auto zone neiter of them had it

 

[SilverBullet00]

The dealership has it.. Some fluid already has it in.. If you look at the back of the bottle, it will say if it has it or not.

 

[97speedster]

Amsoil makes an additive but not necessarily needed. http://www.amsoil.com/storefront/svg.aspx . It refers to it at the bottom of the page.

 

[BennyBlown2v]

The less friction mod you add the more "bite" the clutches will have. The more you put in the more slippery the fluid gets and the less the clutches "bite". As others have stated, some fluid already has additives, some don't. If you have a fluid that doesn't have the friction mod built in, go to your ford dealer and buy a 4oz bottle, should be a just a couple bucks and that's all you need for one fill. Big thing you wanna make sure you do is use 100% synthetic oil - and these cars call for 75w140 not 90, there was a tsb (either for us or some other 8.8 car) a couple years ago and Ford switched to the w140 stuff in the stangs, at least.

 

[4.6andSlicks]

Thanks for the comments.

 

[LaserSVT]

As far as I know it dosent matter weather or not the oil has additives, you are ALWAYS supposed to use friction modifier in a Trac-Loc. Its just how much should be added.