HEy guys, going to change my rear diff fluid today and I got some Valvoline Synthetic 75-140. I have the 3.55 LS rear end. The valvoline specifies Limited Slip on the bottle, do i still need to add friction modifier? In my manual, i was thinking it only said add if it was a Trak-Lok? Are these the same? Thnaks!

 

Yes, you will need a bottle.

 

awesome thanks!

 

I think the "syn power" Valvoline product already contains a friction modifier. Adding a bottle of friction mod will not hurt anything if you want to be sure.

 

You don't need the friction modifier it's already in there

 

Friction modifier was cheap at my dealer, about $4.50 per bottle. I put in 2 bottles in hopes of eliminating my rear end chatter. It helped but did not eliminate it. I used the Vavolyne synthetic 75w140 same as you.

 

Just changed mine last night with royal purple 75-140 which also has the friction modifier in it but still contemplating putting the ford friction modifier for how cheap it is.

 

Thanks for the input guys, I got in there and saw this:

Im thinking that the teeth marks aren't supposed to be on that housing, but i may be wrong. Any input?

 

When I replaced my rear diff cover with a Mag-Hytec cover, I ended up putting Lucas Oil Gear Oil in my diff. Ended up getting a bottle of friction modifier for it too from the local Ford dealer and threw that in. Works great and ended up installing a rear differential temp gauge for the truck while I was at it.

 

No the teats marks shouldn't be there your pinion needs bearings bad to cause that or somebody already rebuilt the diff and reused the diff but u got major issues