# Synthetic Diff Oil



## LS2FAST (Jul 22, 2005)

OK.... does anyone know anything about the ratio of POSI additives and Synthetic Differential Oil, specifically:

Increased or Decreaed Noise
Clunking Sound when accelerating Lightly
What happens if too much
What happens if too little

Please give me any input you may have regarding this.

Thanks in advance All who reply. :cheers


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## Subdriver (Dec 28, 2004)

I believe that GM recommends adding 4oz of friction modifier to two quarts of diff fluid. I've read that if you don't add it the diff will "chatter" in tight turns.

AMSOIL Severe Gear Extreme Pressure Synthetic 75w140 comes with the friction modifier already in it. I use the 75w90 version of this in my Z06 on the track and have never experienced chatter, so I don't add the friction modifier. :cheers


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## LS2FAST (Jul 22, 2005)

OK .... My car is in the shop as of this morning. "clunking" in the rear axle. Dealer said "syntehic will void your warranty if we find anything wrong". Has anyone else heard of this. And does anyone know the exact oil specifications for the differential recommended by Pontiac???


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## Xman (Oct 31, 2004)

The GM rear diff oil is a synthetic. I've never heard that using synthetic will void warantee. I use Royal Purple. So does the GTO Race Car! Skip the mixing of friction modifier and use RP or Amsoil.


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## danrieke (Oct 12, 2005)

Yes, the GM diff oil is synthetic. I'd contact GM about what the dealer said. Warranty work is like medical insurance... the dealer stands to make less $$ from GM doing warranty versus straight from your pocket.


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## Subdriver (Dec 28, 2004)

Pulled this off another GTO thread:

"Straight out of the owners manual.

Rear Axle: 
SAE 75W-140 GL-5 Synthetic Gear Oil (GM Part No. 89021809)."

I'd be really upset by what your dealer is telling you. First, I'd go straight to the service manager, then I'd call Pontiac Customer Service and report the dealership.


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## LS2FAST (Jul 22, 2005)

OK.... should I take the car from the dealer tomorrow and just change the Oil myself and see if the problem is fixed, or should I fight this out with the dealer???

Anyone familiar with Magnusson Moss Act???


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## Groucho (Sep 11, 2004)

Royal Purple needs no friction modifier...


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## GTODEALER (Jan 7, 2005)

Subdriver said:


> Pulled this off another GTO thread:
> 
> "Straight out of the owners manual.
> 
> ...


 :agree .... that's b.s.!


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## dvillar (May 6, 2005)

I'd definatley fight it out


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## Subdriver (Dec 28, 2004)

LS2FAST said:


> OK.... should I take the car from the dealer tomorrow and just change the Oil myself and see if the problem is fixed, or should I fight this out with the dealer???
> 
> Anyone familiar with Magnusson Moss Act???


I've read the act as sometimes dealers will say customers can't use AMSOIL as it will void the warranty (which isn't true). I have enough of an understanding of the act to explain it to my customers who get strong armed by their dealer, but I'm certainly not a lawyer...

I don't think the Act applies in your case though because the dealership is wrong. The diff does come with synthetic in it from the factory.

You can read a good summary of the act here, it really isn't that long:
http://www.ftc.gov/bcp/conline/pubs/buspubs/warranty.htm#Magnuson-Moss


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## LS2FAST (Jul 22, 2005)

OK here is an update.... I sent this letter along with a bottle of the synthetic oil and a bottle of the additive:


Dear Scott,

I am writing you in response to our telephone conversation yesterday. I brought my car into your shop on the morning of October 12, 2005 to complain of a clunking noise in my rear differential. Upon your mechanics review he noticed that I added aftermarket sway bars to the car. From that he eluded that the sway bars could be a possible problem; upon reviewing another GTO from your lot he decided that was not the case. Then, he questioned the type of oil I use. I explained that I use Torco Gear Oil. To be specific following are the specifications:

GM RECOMMENDED: SAE 75W-140 GL-5 Synthetic Gear Oil

CURRENTLY INSTALLED: Torco 100% Synthetic Gear Oil SAE 75W-140 (Meets or exceeds API-GL-6)
Note: For limited-slip or posi-traction differentials use Torco Limited Slip Friction Modifier Type F (for all applications except GM) or Type G (for all GM applications).

Your response was that if I used the Torco instead of the GM oil it will void my warranty. Not only is that untrue, but it is illegal for a warranty to be voided just because an aftermarket part was added to the vehicle. Under Magnusson-Moss Act a dealer must prove, not just vocalize, that aftermarket equipment caused the need for repairs before they can deny warranty coverage.

As expressed in our phone conversation yesterday, I will work with you to resolve this problem. If you feel that I need to change back to the factory GM Oil to “correct” the problem I will do so, but not at my expense. Either you can change the oil and monitor this at your cost or I will have the last company that changed my oil do this change at their expense, which they have already agreed to do.

Please advise the next course of action.

Regards,

SC


So now they are replacing the oil with GM Synthetic, driving it, and then replacing the synthetic a second time. (I agreed to pay for the lube, but not the labor.) If tht doesn't correct the problem, then they will replace the differential.

So I will know in a few days.  

However, the good news is my friend feels bad for me and is allowing me to drive his Porsche Cayenne S until the GTO is repaired.


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## Groucho (Sep 11, 2004)

The way Pontiac service departments are run, GM _deserves_ to go the way of Studebaker.


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## Subdriver (Dec 28, 2004)

I think thats a pretty well written letter, though still b.s. that they are making you put GM lube in at your expense (for the lube). Hope it all works out okay for you. :cheers


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## LS2FAST (Jul 22, 2005)

OK here is the update....

I got my car back today. The dealer did change to the GM Synthetic and the noise did go away. I will drive over the weekend to see if that is the case, and will report to the dealer Monday AM as to my findings over the weekend.

They did not bill me a single penny, nor did I even get a receipt. They just said "here's your car". The tech seems to think the additive was not the right mixture. If he is correct, which it seems like he is... then I will offer to pay the dealership for the service. Since they did not do the original oil change, I feel I should pay them for their time and materials.

All in all this was all blown out of proportion due to the VOID WARRANTY comment.


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## Subdriver (Dec 28, 2004)

Looks like you both are taking a very reasonable approach to the resolution. Glad to see that the noise is gone and I hope it was as simple as the friction modifier wasn't right. I don't know much about the Torco you put in there, but it is possible that it either didn't have, or had too much, friction modifier and what you were hearing was diff chatter. :cheers


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## hardball75006 (Aug 4, 2006)

LS2FAST said:


> OK here is an update.... I sent this letter along with a bottle of the synthetic oil and a bottle of the additive:
> 
> 
> Dear Scott,
> ...


I have never read anything more uninformed in my life. I can't believe this dealerships response to the problem. I guess the rear end in the GTO is so sensitive, that it can only use one type and brand of gear oil? That is a crock! I wish this person knew more about gear oil than he does about spreading B.S.


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## batmans (Aug 16, 2007)

I noticed that many GTO owners pick the Torco mineral oil over the synthetic, which, according to the guy that I spoke at Torco and their online info, provides more protection to the differential.

Is the $10~ cost per bottle the deciding factor to go with the RGO over the SGO?


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