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2005 CTS-"V"
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70 Posts
Discussion Starter #1
Getting ready to change the diff fluid and have a quesrion on which fluid would be best to use. The GM Synthetic Axle lube cost about $29/quart at local dealership which is extremely high compared to other brands. Mobil 1 for example is only $9.99/quart at all auto stores in the area. Is there any reason not to use the Mobil 1 over the GM brand???? They're both synthetic, same weight, etc. With the axle issues we have, I want to make sure I am using best fluid posible.
 

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2005 CTS-"V"
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70 Posts
Discussion Starter #2
From what I have read in the forum, it appears as if Royal Purple is the fluid of choice. Is that correct??
 

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2006 Light Platinum STS-V - 2005 Black Raven CTS-V (gone)
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277 Posts
I prefer Redline 75W-90 gear oil. That was the first mod in both Vs (same carrier) and I've never experienced chatter. Fluid isn't a "magic-mod," but hopefully it gives you some peace of mind over the milky OEM stuff. As a bonus, the Redline already includes the necessary friction modifiers for the clutchpacks in our differentials.
 

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'05 LS6 V Stealth Grey; '14 Z71 SLT Sierra 1500 Stealth Grey
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2,821 Posts
I put royal in mine. It also hast the no additive needed feature. Mine still whines though. It is/ was better then before. 700 miles.
 

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ZIP
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51,864 Posts
I prefer Redline 75W-90 gear oil. That was the first mod in both Vs (same carrier) and I've never experienced chatter. Fluid isn't a "magic-mod," but hopefully it gives you some peace of mind over the milky OEM stuff. As a bonus, the Redline already includes the necessary friction modifiers for the clutchpacks in our differentials.
My 2nd diff has been whiney. While RedLine hasn't gotten rid of the noise, it got me down to VIR for 2 track days and back and the diff is still going strong.

Me likes the RedLine. Royal Purple scares me...
 

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Sedan de Ville, CTS
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4,764 Posts
Take a couple cups of coffee and donuts to your local srvc mgr. Tell him you need his advice. If he is a decent guy, he will be up front with you.

I have not yet asked my (friendly and honest) srvc mgr that specific question. He did volunteer that the GM additive helps the problem. Srvc writer and mechanic told me not to worry if the rear is not chattering.
I was looking for some preventative advice. I still need to ask more specific questions as I do not want to be surprised some day, although I have the GMPP.
 

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'05 LS6 V Stealth Grey; '14 Z71 SLT Sierra 1500 Stealth Grey
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2,821 Posts
What would you define as chattering? I used to hear a grinding like noise when slowing down.
 

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2006 Light Platinum STS-V - 2005 Black Raven CTS-V (gone)
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277 Posts
Aftermarket fluid is not going to correct an issue where you hear gear whine. That either warrants a gearset/differential replacement or a reset/reshim, which can't be done with our cars.

Differential 'chatter' (or moan, depending how you perceive it) is most often heard at low speed maneuvers, such as tight parking lot turns, when the clutches in the differential resist the faster rotation of the outside wheel vs. the inside wheel. This can be a byproduct of using a fluid without proper differential friction modifiers. This additive does not prevent clutch lockup during higher-speed maneuvers that warrant differential engagement.

I encountered this situation once in my Jeep when the friction modifier was overlooked during a rear fluid change. I don't think the issue as as common with our cars if you're using the GM stuff. I thought the newer purple/grape fluid includes some of the additive. However, the factory-fill fluid is a different story. There's an old thread on here started by someone who drained their rear fluid early (~5,000 mis?) and it came out murky-looking, almost cloudy and inconsistent.
 

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'05 CTS-V (sold)
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1,473 Posts
I just changed my Differential and Tranny fluids this morning! Great minds think alike, I guess. I used RP 75w90 for the Diff and Mobil 1 Synthetic ATF for the trans. Also a little Mobil 1 Syn grease for the Hotchkis sways...
 

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05CTS V
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195 Posts
I prefer Redline 75W-90 gear oil. That was the first mod in both Vs (same carrier) and I've never experienced chatter. Fluid isn't a "magic-mod," but hopefully it gives you some peace of mind over the milky OEM stuff. As a bonus, the Redline already includes the necessary friction modifiers for the clutchpacks in our differentials.
Imperator: Is the Redline a synthetic based oil???? Can it be found at advanced, pepboys ect. ??
 

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'05 LS6 V Stealth Grey; '14 Z71 SLT Sierra 1500 Stealth Grey
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2,821 Posts
end up using 2 1/3rd
The couple times I've had it changed, the guys who did it only used 1.5 qts.......
 

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'05 CTS-V (sold)
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The couple times I've had it changed, the guys who did it only used 1.5 qts.......

Nope, about 2 1/3 sounds about right. They must not have let it drain all the way.

The FAQ also says when you're changing the trans fluid, it'll start coming out the fill hole about 1/2 way through the 4th quart. Mine has taken 4 1/2 quarts both times I've changed it.
 

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BANK OWNED!! CTSV & EXT
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1,689 Posts
AMSOIL works fine for me.
 

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2005 CTS-V
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8,363 Posts
I bought and reviewed GM's Specification No. 9986115 for its Axle Lubricant. Based on that review I would NOT use anything other than the recommended recipe of the the GM Axle Fluid plus the GM friction modifier unless and until some other product is actually certified as meeting that GM No. 9986115 specification.

Currently this exlcudes Mobil 1, Royal Purple, Red Line, Amzoil, and everything else for which data specification sheets are readily available.

The GM specification is addition to, and more stringent than the API GL-5 Standard met by some of the alternative products in terms of thermal durablity, axle/gear temperature reduction and axle/gear effeciency (fuel mileage). Additionally and importantly, the GM specification requires friction characteristics for the generally prescribed requirements of locking/limited slip differentials in the base axle/gear lubricant. Thus, by specifying the ADDITIONAL friction modifier additive for the CTS-V differential, GM is effectively requiring more friction modification than that generally included in other products listed as being appropropriate for use in limited slip differentials. Stated differently, if you use a non-GM (substandard) axle/gear lubricant you still "add the additive."
 

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ZIP
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51,864 Posts
I bought and reviewed GM's Specification No. 9986115 for its Axle Lubricant. Based on that review I would NOT use anything other than the recommended recipe of the the GM Axle Fluid plus the GM friction modifier unless and until some other product is actually certified as meeting that GM No. 9986115 specification.

Currently this exlcudes Mobil 1, Royal Purple, Red Line, Amzoil, and everything else for which data specification sheets are readily available.

The GM specification is addition to, and more stringent than the API GL-5 Standard met by some of the alternative products in terms of thermal durablity, axle/gear temperature reduction and axle/gear effeciency (fuel mileage). Additionally and importantly, the GM specification requires friction characteristics for the generally prescribed requirements of locking/limited slip differentials in the base axle/gear lubricant. Thus, by specifying the ADDITIONAL friction modifier additive for the CTS-V differential, GM is effectively requiring more friction modification than that generally included in other products listed as being appropropriate for use in limited slip differentials. Stated differently, if you use a non-GM (substandard) axle/gear lubricant you still "add the additive."
And the things still blow up. I think you could piss in it and it still won't matter.
 
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