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Discussion Starter #1
Im changing all the fluids before my first race and just wondering what you all do about friction modifier in a stock rear end? use it or not, and if you do how much. oh, and I have 2 quarts of Royal Purple 75-90. I was told that most gear oils have it already in it which is why I now have this question.
 

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When I did my first diff fluid change with the stock T'loc, I used Mobil 1 with the Ford modifier, even though I believe the Mobil 1 stated it contained the additive.

When we changed the gears and installed an Eaton LSD, Strano and Eaton recommended a regular petroleum based fluid. IIRC, we used the LS formula Valvoline plus added the friction modifier.

It may work fine just using the LS spec fluid. The back of the bottle should say if it's compatible with clutch type diffs. Can't see a real downside in a race application. Noise and chatter on some turns?
 

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I leave it out with fluids like that unless the diff chatters in corners, in which case I'll add half a bottle.
 

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Discussion Starter #4
ok. thanks guys.
 

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I use Valvoline synthetic blend 75w90 with no friction modifier and no chatter when shimming. With new clutches it chatters a little so I add some if that happens.

In my Corvette I ran Mobile 1 without the modifier and no chatter on it either.
 

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No FM needed with the Royal Purple fluid.
 

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I use mobil 1 and have always added the modifier. I know it works and don't want to have to go back and add it later if I try without it and find out it got noisy.
 
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