# GM friction modifier



## bobh (May 4, 2009)

This isn't available any more so what other brand is ok to use. Torco isn't local to me. Anything from NAPA or other parts houses?


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## Rukee (Feb 8, 2007)

Available from NAPA, not sure if it's approved for the new GTO but....

NAPA part # 402508 K & W Chemicals.

Attributes 
Container Size : 7 oz
Gear Oil Style Name : Gear Oil Additive
Synthetic : No
Gear Oil Application : Limited Slip Gear Oil Additive
Manufacturer : CRC


Warranty 
2 Years from Date of Manufacture


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## bobh (May 4, 2009)

I just wonder if that is for the clutch type instead of the cone type limited slips.


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## svede1212 (Nov 1, 2005)

Be aware you need the "FM" Ford type modifier not the GM for our differentials. Perhaps Ford may have it?


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## B-ville Goat (Oct 5, 2008)

You can mail order from Torco, just did this myself.


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## bobh (May 4, 2009)

I ended up buying a little bottle made by Kendall. The parts store sells a lot of motorcraft products and they sell this in place of the motorcraft product. Smells really really strong.


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## GTO JUDGE (May 14, 2005)

bobh said:


> I ended up buying a little bottle made by Kendall. The parts store sells a lot of motorcraft products and they sell this in place of the motorcraft product. Smells really really strong.


The rear end is very sensitive to FM. Any FM used must conform to GM's recommendations or you'll end up with noises and eventually failure. This type FM is NOT sold over the counter in parts stores. You may want to make sure this product by Kendall conforms to GM's specs. IMO: If it did this issue would be solved for many. It's NOT.


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## svede1212 (Nov 1, 2005)

GTO JUDGE said:


> The rear end is very sensitive to FM. Any FM used must conform to GM's recommendations or you'll end up with noises and eventually failure. This type FM is NOT sold over the counter in parts stores. You may want to make sure this product by Kendall conforms to GM's specs. IMO: If it did this issue would be solved for many. It's NOT.


It really isn't GM specs it's Ford/Dana. The GM specs are for every other GM car but our Aussie ones.


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## bobh (May 4, 2009)

Well so far it's ok. Will be able to tell better after the 1200 mile trip this weekend.


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## GTO JUDGE (May 14, 2005)

svede1212 said:


> It really isn't GM specs it's Ford/Dana. The GM specs are for every other GM car but our Aussie ones.


Yep it's Dana's but the GM numbers reflect Dana's requirement. Most don't know its Dana. 

The entire rear end is one part number this is why the entire rear was replaced instead of rebuilt. Dana has their own specs. The GM FM modifier Number is for the Dana rear, its a GM number. Its just semantics but most have no clue, easier to say GM. 

Those looking to replace rear end oil:
add 1 oz. of Limited-Slip Differential
Friction Modifier 7098
(GM Part No. 89021958) cannot find? Use an equivalent of that FM.


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## svede1212 (Nov 1, 2005)

GTO JUDGE said:


> Yep it's Dana's but the GM numbers reflect Dana's requirement. Most don't know its Dana.
> 
> The entire rear end is one part number this is why the entire rear was replaced instead of rebuilt. Dana has their own specs. The GM FM modifier Number is for the Dana rear, its a GM number. Its just semantics but most have no clue, easier to say GM.
> 
> ...


You have to be clear though if you use Torco for instance the GM(GM) modifier is wrong and the FM(Ford) modifier is correct.


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## GTO JUDGE (May 14, 2005)

svede1212 said:


> You have to be clear though if you use Torco for instance the GM(GM) modifier is wrong and the FM(Ford) modifier is correct.


I have no idea if Torco is correct for this rear. I am leery on any oils with the FM in it for this rear. Do you have a Ford # for their FM for this rear? You're saying any Ford FM will work? Does Ford sell just the FM like GM once did?


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## bobh (May 4, 2009)

After 1200-1300 miles everything is still ok.


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## svede1212 (Nov 1, 2005)

GTO JUDGE said:


> I have no idea if Torco is correct for this rear. I am leery on any oils with the FM in it for this rear. Do you have a Ford # for their FM for this rear? You're saying any Ford FM will work? Does Ford sell just the FM like GM once did?


I do not have a Ford number as I've always used Torco. Back quite a few years ago there was a lot of discussion about the rear end on other forums. DiffTech is an Australian company that sold sold gears and is involved with the Australian car community. I have their 3.91 gears. They said that Torco oil and their FM modifier were the preferred gear lubricant and is what is run down there. It took twice the amount of GM modifier to get the same results most likely because this rear end is the only GM one like it. Our cones are more like the Ford. The Torco FM modifier is a separate bottle that is added after. Oils like Royal Purple with modifier included IMHO is absolutely the wrong way to go and I'll explain why.

I have the "spring kit" that increases cone pressure. GM wanted weak springs as it made it easier to make a quiet albeit one more prone for one wheel burn outs. Because the cone system is just a friction fit cone wear, springs, etc make the amount of FM variable. The way to add it is to put in too little and take the car for a short spin to mix it and try some slow sharp turns. If the rear end makes noise like marbles or popping on slow turns you add a little more FM and repeat. You keep doing that until it stops. Some diffs don't take the full amount and some take more. If you add too much you won't notice any noise but you can get one wheel burn outs. If fact there is no "exact" amount of modifier to add. Premixed may or may not have too much for your diff. You want the least amount that allows the cones to slip quietly under normal turning.


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## GTO JUDGE (May 14, 2005)

Good information to have for the future. 
So....
Torco FM modifier for Ford application as an additive.
Torco oil for Ford.


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## svede1212 (Nov 1, 2005)

The Torco that seems to work the best is 85w-140 with Torco Type F modifier. Make sure you use the RGO and not the SGO.


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## 84racebird (Jan 4, 2005)

I've had rearend noises for years with my '04 which has about 61k miles. I went to two different dealerships today looking for the correct fluids. I was told different things at each dealer and I'm trying to figure out what to do. The second guy admitted to not understanding what was needed and promised to dig into it some more and call me next week with information. Apparently the gear lube is still available for $40 a quart. It's expensive, but I want to see if it solves the problem. The FM part number has been changed and is now crossed to 75w-90 gear lube with FM additive for around $30 a quart. Can anyone tell me if the 75w-90 is what should now be used in these cars?

I have changed the fluid 3 times already. The first time I used Amsoil with their FM. When that started making noise, I changed it and used the GM FM (not sure if it was the right PN) with Mobil 1. The third time was Mobil 1 with GM FM again. It seems like it will stay quiet for 1,000 miles and then it goes back to clanking, grinding, and popping when making slow turns.


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## svede1212 (Nov 1, 2005)

. . . and you never tried the recommended Torco. It's fairly cheap on Amazon. Be warned though that if the problem is whine the gears would have to be replaced and shimmed correctly to likely solve it


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## 84racebird (Jan 4, 2005)

No whine at all. Everything is good when driving straight and at all speeds. The rear just doesn't like turning. I just started researching this and saw the posts about the Torco product. I will dig into that a little more. I plan on doing the fluid change in a couple weeks, so I have some time to decide what to do.


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## svede1212 (Nov 1, 2005)

Read the method in post #14. Adjusting the FM is an important step that most skip over and dealers know nothing about.


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## NucciGOAT (Dec 10, 2013)

So let me get this straight, we have a Dana rear end on our cars? Or is it a GM built rear end that mimics the Dana? 

And when I go to flush the fluid I have to go by ford specs and not the GM recommended specs for our car? Why would GM put out the wrong specs for our car and not realize it eventually ten years later?

The previous owner changed the diff fluid in my car twice in 40k miles cause he was extremely anal. I need to call him and see what he used. I want to say he put RP in it. Then AMS in it. I have no noise what so ever tho and def lay down two black lines on burnouts.


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## GTO JUDGE (May 14, 2005)

NucciGOAT said:


> So let me get this straight, we have a Dana rear end on our cars? Or is it a GM built rear end that mimics the Dana?
> 
> And when I go to flush the fluid I have to go by ford specs and not the GM recommended specs for our car? Why would GM put out the wrong specs for our car and not realize it eventually ten years later?
> 
> ...


The rear ends were built by Dana. The reason GM replaced the rears instead of repairing them was it was a single part number, as a single part number GM back charged Dana through warranty. There is a lot of money to be made in back charging vendors, A LOT. 

Dana built many different rear ends. Oil requirements on many were the same. The FM used in the rear end for the GTO was the same kind built for Fords. The GTO is no longer produced. Makes sense to eliminate the GM part number for the FM if the same can be found through Ford. Would seem to me if you took your car to the GM dealer and he doesn't have NOS on the shelf a trip to the Ford dealer to obtain the FM would be in order. (Just surmising here but would make sense not to inventory FORD FM in a GM facility when it can be gotten locally? )

This was not a GM thing it was a DANA requirement. GM stocked the FM under their name and with it they need a part number. GTO Dana rears no longer are made. Being they both use the same FM..... hence use Ford. Unless you find the CORRECT FM in an over the counter oil as some suggest have it. 

Take Svede's advice >>> The Torco that seems to work the best is 85w-140 with Torco Type F modifier. Make sure you use the RGO and not the SGO. 

Unless the car was raced used hard or abused, there is no reason to keep changing the oil out. Seems a lot of extra $ and time was wasted doing so.


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## NucciGOAT (Dec 10, 2013)

GTO JUDGE said:


> The rear ends were built by Dana. The reason GM replaced the rears instead of repairing them was it was a single part number, as a single part number GM back charged Dana through warranty. There is a lot of money to be made in back charging vendors, A LOT.
> 
> Dana built many different rear ends. Oil requirements on many were the same. The FM used in the rear end for the GTO was the same kind built for Fords. The GTO is no longer produced. Makes sense to eliminate the GM part number for the FM if the same can be found through Ford. Would seem to me if you took your car to the GM dealer and he doesn't have NOS on the shelf a trip to the Ford dealer to obtain the FM would be in order. (Just surmising here but would make sense not to inventory FORD FM in a GM facility when it can be gotten locally? )
> 
> ...


Very interesting, thankyou for the information. So they were rear ends built by Dana and GM used Dana as the supplier (or Holden) for the GTO rear? So does that mean that ford 9 rears can be bolted up because we have Dana's?? I've heard the rear is very weak in our car and on an M6 like mine we need to upgrade and the 10 bolt is not enough. 

Yes it is totally not needed and your not gna catch me changing it like that, but I'm glad he did!! Lol more power to him. Took care of what is now my car!! Lol

And yea I know there is good profit to be made charging back suppliers. I am a quality engineer and I charge back suppliers all the time. But it's not really profit per say, it's just you don't pay the warranty/repair costs.. They do. So it's money saved.


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## GTO JUDGE (May 14, 2005)

NucciGOAT said:


> Very interesting, thankyou for the information. So they were rear ends built by Dana and GM used Dana as the supplier (or Holden) for the GTO rear? So does that mean that ford 9 rears can be bolted up because we have Dana's?? I've heard the rear is very weak in our car and on an M6 like mine we need to upgrade and the 10 bolt is not enough.
> 
> Yes it is totally not needed and your not gna catch me changing it like that, but I'm glad he did!! Lol more power to him. Took care of what is now my car!! Lol
> 
> ...


GM used Dana rears for these cars. Will a Ford rear end bolt up? I dunno could be yoke issues? Axle and wheel issues? 

I worked for Dana, we assembled Mack Truck components on chassis and built rear ends and axles. Dana made a fortune back charging suppliers that sent faulty parts, they made a lot of money back charging Mack Truck too for incorrect applications and parts Mack would send from suppliers they got parts from that were incorrect. It was a whole other business in itself.


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## NucciGOAT (Dec 10, 2013)

GTO JUDGE said:


> GM used Dana rears for these cars. Will a Ford rear end bolt up? I dunno could be yoke issues? Axle and wheel issues?
> 
> I worked for Dana, we assembled Mack Truck components on chassis and built rear ends and axles. Dana made a fortune back charging suppliers that sent faulty parts, they made a lot of money back charging Mack Truck too for incorrect applications and parts Mack would send from suppliers they got parts from that were incorrect. It was a whole other business in itself.


Haha! That's funny man small world. I work for continental, (formerly siemens) and my product is Diesel PCR injectors for said Mack truck engines, but mainly Navistar or (international) is our main customer.

I mean you can charge a supplier for downtime and missed profitability by not being able to produce and sell parts, because they sent faulty stuff and you couldn't build. But that is not common. I mean generally not every lot they shipped is bad. So you have other lots to keep building. The only time you can charge for downtime etc.. Is if you are truly shut down. That doesn't happen often, and even then your still coming out even cause your only getting paid for the production you lost. Your not really coming out with huge profits like you say. Your just not taking a loss.. You already paid for those parts your charging back. You just get your money back. Maybe you were giving bad info or interpreted it wrong. 


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## Red Bearded Goat (Mar 19, 2007)

GTO JUDGE said:


> Take Svede's advice >>> The Torco that seems to work the best is 85w-140 with Torco Type F modifier. Make sure you use the RGO and not the SGO.
> 
> Unless the car was raced used hard or abused, there is no reason to keep changing the oil out. Seems a lot of extra $ and time was wasted doing so.


The rear diff oil should be changed about every 30k miles via normal driving.... more frequent if abused via track usage or frequent stop light burn out jackassery. Torco RGO 85w-140, along with the Type F (Ford) FM can be ordered directly from Torco. With a stock diff cover, it takes slightly less then 2 liters of the RGO and about a half bottle of the FM. If you have a Harrop cover, it will take almost double.


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