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No there is no recommended one altho ones (that are inferior IMHO) like Royal Purple are premixed. Besides spotty results the reason I wouldn't use a premix is that the amount of modifier varies from car to car. The way to do it is put in your Torco, add about half the recommended amount of FM modifier, drive it a bit to mix and do a few slow, hard turns. If the rear end clicks and pops add some more modifier and repeat. You want to add just enough to have it not make the clicking, popping noise. Too much and you get a one wheel burnout. Shops in Australia report that the amount of modifier runs from a little over half to up to one and a half of the recommended amount to get good results.
 

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I need to do my diff fluid and want to use something that already has the FM in the oil. Is there anything you guys could recommend?

Thanks
The GTO diff is quite sensitive. Some have different results than others. I've tested a few already. GM stuff, Mobil 1, Royal Purple to Torco. I've had the best luck with Torco. Take it from me my car is/was the most universal car here.
 

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Your best bet is to pass on the "pre-mixed" fluids. Go with a decent 75w-140 like mobil, royal purple, etc and use a friction additive. GM calls for 1oz of modifier. As stated above, too much and you'll get a one tire fire, however too little or none at all and you could cause serious issues.
 

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Former Moderator
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4,081 Posts
Your best bet is to pass on the "pre-mixed" fluids. Go with a decent 75w-140 like mobil, royal purple, etc and use a friction additive. GM calls for 1oz of modifier. As stated above, too much and you'll get a one tire fire, however too little or none at all and you could cause serious issues.
Too little isn't that serious of an issue. You'll get the chattering/popping noise to remind you to add a little more but it's not breaking anything. I'd rather edge up to the right amount than over do it because it's hard to know if you did sometimes.
 

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I plan on changing the diff fluid this week. I cant decide to use the gm stuff (89021809) or go with Torco.. Also do i need the Torco type G or type F? I hear i need F but the website says type G for gm. Thanks
 

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yes you are correct. I should read before i post.

"Recommended for use in Ford, Mazda, Chrysler, Toyota and all other limited-slip and posi-traction applications including late model Pontiac GTO. Not for use in all other GM applications. Treatment level is 2% to 6% by volume"
 
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