# Gear oil question



## Lukemo2 (Apr 13, 2010)

I'm going to change the differential fluid in my '04. I've done a lot of reading on this, and I've learned that* if I don't use the GM part or Royal Purple*, I have to add friction modifier to the oil. 

I have not been able to find Royal Purple or the GM stuff in any of the stores or dealerships around here. I have purchased Mobile 1 full synthetic 80W140 gear oil, but I don't know what the friction modifier is called, how much to use, and how to use it. 

Can anyone enlighten me?

Thanks~


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## mikes06goat (Jan 13, 2009)

They come in bottles of like 4-7 ounces. I've never been in a parts store that doesn't carry them. Even the Dodge dealership in my town carries it and it's all the same stuff. You can use a whole bottle. You can get it from summit. I believe they carry REDLINE.
K&W makes one, ATP makes one. Is their an O'reillys in your town?

Many synthetic gear lubes have the limited slip additive built in so I would read the label on the Mobil1 that you purchased and see what it says.

Here the GM part number:
GM Performance 1052358 Limited Slip Lubricant Additive 4oz


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## jpalamar (Jul 22, 2008)

I used RP in my trans and diff. No complaints after 20k miles after the chainge.


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## GM4life (Mar 18, 2007)

The original specs for the GTO was:
75w-140 synthetic for the gear oil and 1oz for friction modifier

Royal Purple is a hit and miss, I had problems with it and others have too. Torco Type F seems to work best and thats what I use along with their limited slip additive. I used the whole bottle of limited slip additive without problems.


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## srs7324 (Jul 8, 2010)

*Pontica GTOGear Oil*

75w140 Mobile 1 Sythetic with a small amount of friction additive was what I used.

20 dollars a bottle at Advance. 

All others appeared to be non synthetic and just run of the mill oil with no aditivies or additional properties.

NAPA did carry a friction modifier, but they have to order it overnight.


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## srs7324 (Jul 8, 2010)

*Gear Oil Additives*

After reading up on a number of premium Synthetic Gear Oils, they all basically state that a Friction Modifier is not necessary and may cause harm if added.

NOTE: Synthetic Gear Lubes do not require the use of this additive. 
However, not all differentials respond the same and if chatter is noticed, the addition of Friction Modifiers will eliminate it. 
For chattering differentials not running Synthetic Gear Lube, this type of product is an excellent solution to the problem.

So it is my assumption that if you use run of the mill 75W140 gear oil, a Friction modifier is necessary, but if you purchase a Synthetic such as Mobile 1 or AMSOIL it is only needed on a case by case basis.

Just an FYI.


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## Lukemo2 (Apr 13, 2010)

*To add or not to add... that is the question.*

Here is what I found on the mobile 1 website:

"Mobil 1 Synthetic Gear Lube 75W-140 LS contains special friction modifiers designed for limited slip-type differentials. In most applications, the addition of special LS (limited slip) additives is not required. For axles requiring the highest level of limited-slip performance, OEM specific LS additives can be added to this fluid."

I am going to add about an ounce of friction modifier. I think I'll just go to the local dealer and order the GM performance limited slip additive. I would probably be safe without it, but I don't want to risk it.


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## ROBSGTO (Jul 6, 2008)

Wasn't tryting to highjack your thread,post was deleted.

Hope you get your answer,but on the other forum there is a GM parts sponsor that can get you the new GM fluid with friction modifier already in it.


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## GM4life (Mar 18, 2007)

The important thing is manufactures of gear oils do not build the rear ends, how would they know what the rear end needs or don't need. I think GM/Dana does more testing on the rear end than a gear oil manufacture. They know whats best for it. You run a diff without sometype of LSD additive if you want to and see how much noise its going to make. Our rear ends are a cone type not a clutch type. Thats the reason why people use a type F friction modifier than the type G for GM rears with Torco.


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## NEXSTAR7 (Jan 28, 2007)

i went with amsoil 75w 140 and there friction modifier its been a month. no problems


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## Lukemo2 (Apr 13, 2010)

GM4life said:


> The important thing is manufactures of gear oils do not build the rear ends, how would they know what the rear end needs or don't need. I think GM/Dana does more testing on the rear end than a gear oil manufacture. They know whats best for it. You run a diff without sometype of LSD additive if you want to and see how much noise its going to make. Our rear ends are a cone type not a clutch type. Thats the reason why people use a type F friction modifier than the type G for GM rears with Torco.


I believe you know what you're talking about, and from reading your other posts, you seem very knowledgeable and educated. So, I followed your suggestion and was looking at the Torco LS friction modifier on their website. It says the Type G is for use with GM vehicles and the Type F is for use with everything else. But you said you used the Type F in your GTO? 

See, a guy like me would look at the product descriptions and think "hmm, this says it's for GM vehicles" and I'd buy it. But you say that the Type F is the way to go?


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## GTO JUDGE (May 14, 2005)

GM specifically states to use the GM FM, 1 oz of it. Many gear oils have FM in it however with this type rear GM is explicit in adding that type FM. Failure to adhere to this type FM in this type rear could in time lead to the rear end whine. This FM is designed for this rear end. 

FROM THE MANUAL:

SAE 75W-140 GL-5 Synthetic Gear
Oil (GM Part No. 89021809). With a
complete drain and refill *add 1 oz.
(25 ml) of Limited-Slip Differential
Friction Modifier 7098
(GM Part No. 89021958). *

DO NOT RELY on just an oil with FM in it. Add the equivalent gear oil with this specific FM.


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## GTO JUDGE (May 14, 2005)

Lukemo2 said:


> I believe you know what you're talking about, and from reading your other posts, you seem very knowledgeable and educated. So, I followed your suggestion and was looking at the Torco LS friction modifier on their website. It says the Type G is for use with GM vehicles and the Type F is for use with everything else. But you said you used the Type F in your GTO?
> 
> See, a guy like me would look at the product descriptions and think "hmm, this says it's for GM vehicles" and I'd buy it. But you say that the Type F is the way to go?


I agree GM knows his stuff. 

EXAMPLE;
On transmission OIL bottles it says use DEXRON VI in MOST transmissions on 2006 and later model GM cars. HOWEVER the operative word is MOST. The T-56 is not like MOST transmissions. This type transmission fluid will ruin a T-56 transmission. DON'T always rely on information on an oil bottle. Often times there is generic wording on bottles, MOST is the key word. This car is vastly different then the run of the mill car out there. READ YOUR OWNERS manual for specifics. Don't chintz on oils or FM, use the equivalent of what the manufacture calls for.


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## Lukemo2 (Apr 13, 2010)

GTO JUDGE said:


> GM specifically states to use the GM FM, 1 oz of it. Many gear oils have FM in it however with this type rear GM is explicit in adding that type FM. Failure to adhere to this type FM in this type rear could in time lead to the rear end whine. This FM is designed for this rear end.
> 
> FROM THE MANUAL:
> 
> ...


I definitely do not want to cut any corners. That is why I haven't changed it yet. I want to be absolutely sure I'm doing it right. 

However, I have an '04, and I have read my manual a lot, and it doesn't say anything about a friction modifier. It says "Rear Axle: SAE 80W-140 Synthetic Axle Lubricant (GM Part No. 89021809)" and thats it. 

This is what's confusing me: Most forum enthusiasts say to put in friction modifier, some say don't. Some say 1oz, some say the whole bottle. Some say it's ok to use oil other than the GM part, some say it's not. 

From what I can gather, a friction modifier is needed (even though my manual doesn't mention it). Also, I should use the GM oil and NOT something after market. 

Is there any chance that the '04's would NOT require a friction modifier while the '05-'06's would? The information I'm looking at in my manual is in the "Recommended Fluids and Lubricants" section on page 6-14. 

Maybe GM just failed to put it in the manuals for '04 and then added it to the later models? 

I guess the big question is; can the friction modifier HURT my differential if it ISN'T required??

Damn, I sound neurotic.... Am I over-thinking this?:confused


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## jpalamar (Jul 22, 2008)

I just checked my 04 manual as well. It does only say to use "SAE 80W-140 Synthetic Axle Lubricant (GM Part No. 89021809)." Weird.


And just broke 2000 posts!


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## pctek (Jul 18, 2010)

I didnt want to start another thread, I too want to change my gear oil following this guide: Differential, Manual Transmission & Engine Oil changes

Now reason for this is when Im driving pretty much slow when stopping and going sometimes seems like if i let go of the gas, hit the brakes and then let go and start hitting the gas a combination of these, I hear like a clunking noise from the rear of car, like something has play/loose. I did a google search and alot of people are saying change out the diff oil. To me that doesnt makes sense for a loose clunking noise seems like more of taking care and making the common whine noise more silence? 

Also do I lift the car with front and rear floor jacks to make the car even for diff change and wheres a good spots for the jacks?


What you guys think?


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## GM4life (Mar 18, 2007)

Lukemo2 said:


> I believe you know what you're talking about, and from reading your other posts, you seem very knowledgeable and educated. So, I followed your suggestion and was looking at the Torco LS friction modifier on their website. It says the Type G is for use with GM vehicles and the Type F is for use with everything else. But you said you used the Type F in your GTO?
> 
> See, a guy like me would look at the product descriptions and think "hmm, this says it's for GM vehicles" and I'd buy it. But you say that the Type F is the way to go?


Thank you. I do alot of research, talking with people and work on my own car. I like to get the best info I can to help our members out.

Yes sir, use Type F when using Torco. It is more suted for use in our cone type LSD.


Lukemo2 said:


> I definitely do not want to cut any corners. That is why I haven't changed it yet. I want to be absolutely sure I'm doing it right.
> 
> However, I have an '04, and I have read my manual a lot, and it doesn't say anything about a friction modifier. It says "Rear Axle: SAE 80W-140 Synthetic Axle Lubricant (GM Part No. 89021809)" and thats it.
> 
> ...


The service manual calls for 1oz of friction modifier when using GM type gear oil. Torco says to use the whole bottle witch I done. I haven't had any problems with it. The only issue with using too much FM is that you may have one wheel peel and too little to none results in noise going around corners.


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## GTO JUDGE (May 14, 2005)

I am fairly certain the rear ends on all 3 years are the same, if so use the same guidelines on the '04 as '05-06. Anything more than 1 oz is over kill. I believe GM sells that FM in a larger than 1oz bottle (I had gotten one once) but cannot fully recall the exact oz bottle on the GM oils. I have no experience with Trico saying to use a whole bottle of FM. I do know it stinks, I placed the container of it in an empty coffee can to avoid spilling it. 

Just use the equivalent of the GM oil and 1oz of FM and you will be fine.


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## Lukemo2 (Apr 13, 2010)

Sounds like a plan. Thanks, guys.


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## Lukemo2 (Apr 13, 2010)

So... I went on gmpartsdepartment.com to order the friction modifier (GM Part No. 89021958), and it has been discontinued. It says "Part number 89021958 was superseded by part number 88862624". I called them, and the guy told me that GM has replaced the friction modifier with a new 75W90 GEAR OIL that doesn't need the friction modifier and is ok to use in my GTO. 

My head just about exploded...

Oh, and they still sell the original 80W140 gear oil (89021809) that requires friction modifier.


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## ROBSGTO (Jul 6, 2008)

Lukemo2 said:


> So... I went on gmpartsdepartment.com to order the friction modifier (GM Part No. 89021958), and it has been discontinued. It says "Part number 89021958 was superseded by part number 88862624". I called them, and the guy told me that GM has replaced the friction modifier with a new 75W90 GEAR OIL that doesn't need the friction modifier and is ok to use in my GTO.
> 
> My head just about exploded...
> 
> Oh, and they still sell the original 80W140 gear oil (89021809) that requires friction modifier.


There are plenty of guys using the 75W90 without issues.I've heard the Corvette guys rave about it so if it's good enough for a Vette I thinks it's good enough for our GTO's.

That being said I just ordered the Torco RGO with Type F Modifier.


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