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2004 CTS-V
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358 Posts
Discussion Starter #1
Ok, my new rear diff, which has all of 1,500 miles on it, is getting loud already. It's whining at 47-55mph and then again at 80mph in 6th.

Since the dealer JUST put it, as well as a new transmission, in the V, I'm going to try a few things before I take it back.

I'm going to pick up two quarts of Royal Purple 75w140 this afternoon and swap the fluid in the diff sometime this week. I'll report back and let you guys know if it helps with the whining. Mine gets loud when things heat up, so I'm hoping this weight oil helps.

Oh, and BTW, Pepboys is offering $10 off of any purchase of $30 or more. Because this stuff is $18.99 a quart regularly, the coupon's going to come in handy.
 

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'05 CTS-V, Powered by Chevrolet
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835 Posts
I wouldn't expect an gear oil change to fix a problem. FWIW, I used Amsoil 75W-90 after 2500 miles in my replacement diff. Mine begins to whine after a long drive where it gets some heat in it.
 

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Premium Member
2005 CTS-V
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8,363 Posts
Ok, my new rear diff, which has all of 1,500 miles on it, is getting loud already. It's whining at 47-55mph and then again at 80mph in 6th.

Since the dealer JUST put it, as well as a new transmission, in the V, I'm going to try a few things before I take it back.

I'm going to pick up two quarts of Royal Purple 75w140 this afternoon and swap the fluid in the diff sometime this week. I'll report back and let you guys know if it helps with the whining. Mine gets loud when things heat up, so I'm hoping this weight oil helps.

Oh, and BTW, Pepboys is offering $10 off of any purchase of $30 or more. Because this stuff is $18.99 a quart regularly, the coupon's going to come in handy.
The traditional response to a new differential that makes noise is to check the internal gear back lash/clearances/preload adjustments immediately. I am not sure why we abandoned that standard procedure in favor of a search for a magic fluid.
 

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2016 ATS Premium 6-spd MT
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14,075 Posts
If the dealer did it, why not just take it right back there and at least get it on record that it's whining again?

IMHO, changing diff fluid is a good thing, but it's like snake oil for whining ... again, that's IMHO.
 

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2018 CT6E, old: 2014 XTS Vsport, 2005 CTS-V, 2004 CTS-V.
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2,732 Posts
If it started making noises the heavier Royal Purple might do the trick. :)

Norm
 

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'05 CTS-V, '00 SLS, 98 SLS, 89 Eldo, '80 Eldo
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4,001 Posts
Mine only started whining after the specter bushings. I put in Amsoil, I think it was 75W-110. After a few hundred miles, its much better. Not enough to bother me, and I like it quiet.

That said, I'd go with Darkmans suggestion.
 

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'05 CTS-V, Powered by Chevrolet
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835 Posts
The traditional response to a new differential that makes noise is to check the internal gear back lash/clearances/preload adjustments immediately. I am not sure why we abandoned that standard procedure in favor of a search for a magic fluid.
It's being abandoned due to dealerships and manufacturers finding it easier to swap out parts as assemblies instead of fixing them at the dealer.

I wonder how hard it would be to get the gear and bearing parts to rebuild a CTS-V/Getrag differential? To rebuild a Ford 8.8" rear, you can get the parts at WaWa with a cup of coffee and it will outlast the V.
 

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852 Posts
My car is too loud to hear the wining.. but mine has wined ever since Ive had it.. going on four years now.. Never had a problem it.. I havent even changed the fluid in my diff in thousands of mile.. hope thats not a bad thing!!
 

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2004 CTS-V
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358 Posts
Discussion Starter #11
I called the dealership. They said swapping the fluid wouldn't be an issue for my warranty. They even want me to call them and tell them if it help. They said, if not, bring it in and they'd check it out.
 

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2004 CTS-V
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358 Posts
Discussion Starter #12
Alright, well I spent all day saturday at InTune Motorsports in Charleston, Tn. Scott let me thow the V up on a lift while he was working on a stock car and I put the 75w140 Royal Purple in. In short, while I still have some rear end whine at certain speeds, I have noticed a marked difference in the whine I'm hearing from the rear end once the car heats up. Beforehand, after things heated up, I'd get a really pronounced whine in 5th and 6th under light throttle at around 50 and again at around 65. Now, it's noticably quieter.
 

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2011 CTS-V
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236 Posts
i've been hesitant to do anything to help the wheel hop because i don't want to make the diff whine louder... its good to know that some heavier fluid will help
 

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Premium Member
2005 CTS-V
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8,363 Posts
After all these years I am just now beginning to undestand the infamous STP oil treament phenomenon.
 

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05 CTS V
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600 Posts
Has anyone used Redline products?? I am thinking the Amsoil, Royal Purple & Redline 75-140 + additive are all the same. I plan on doing the BMR pinion support, UUC diff bushing and gear oil change while I am down there. Any one of those three synthetics better than the other??
 

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2005 CTS-V, Black
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2,165 Posts
Has anyone used Redline products?? I am thinking the Amsoil, Royal Purple & Redline 75-140 + additive are all the same. I plan on doing the BMR pinion support, UUC diff bushing and gear oil change while I am down there. Any one of those three synthetics better than the other??

I for one like my Royal Purple Synthetic in the diff...but I feel like more people overall use the Amsoil. I use Redline in my Power Steering though. Preference I guess.
 

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2006 CTS-V
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1,415 Posts
The traditional response to a new differential that makes noise is to check the internal gear back lash/clearances/preload adjustments immediately. I am not sure why we abandoned that standard procedure in favor of a search for a magic fluid.
+1 to that. new diff fluid shouldn't be a concern... unless you don't have any left in the diff :thepan:

clearances... think it needs to be shimmed for correct ring gear clearance?
 

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Premium Member
2005 CTS-V
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8,363 Posts
+1 to that. new diff fluid shouldn't be a concern... unless you don't have any left in the diff :thepan:

clearances... think it needs to be shimmed for correct ring gear clearance?
Well I think it has to involve clearances, but what do I know?

In in the old days when we all had solid lifters that got noisey I was the fool over in the corner of garage adjusting the valve clearances while the smart guys were loading up their crankcases with STP oil treatment.
 

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06 CTS-V (sold)
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680 Posts
I am thinking the Amsoil, Royal Purple & Redline 75-140 + additive are all the same.
Totally not the same. AMSOIL primarily uses a Group IV, PAO basestock for its diff fluids (and most of its oils and tranny fluids), but likely blends in a little Group V polyol ester to modify the PAOs coefficient of friction and impact on seals. Red Line uses a Group V, polyol ester basestock for its fluids. RP won't say what it uses. I suspect they use a blend that is primarily a Group III, highly hydro-processed mineral oil basestock, with some Group IV and V blended in. Many trade offs in how the fluids are blended together.

For an interesting read on the most common 75w90s on the market, check out this AMSOIL commissioned study:
AMSOIL Gear Lube “White Paper” (2 MB pdf file)
 

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2018 CT6E, old: 2014 XTS Vsport, 2005 CTS-V, 2004 CTS-V.
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2,732 Posts
Comissioned study?! How bias is an in house test? If AMSOIL is so superior over their 25+ year life then why are they and the others not a required? Probably because they are not needed for the daily driver/weekend warrior track stuff.

Sounds like some snake oil to me! :)


Norm
 
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