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06 CTS-V (sold)
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Discussion Starter #1
All,
I changed out my factory fill diff fluid with AMSOIL Severe Gear Extreme Pressure Synthetic 75w90 a few weeks ago, sampled the stock fluid and submitted it to Blackstone Labs. The fluid had 10,636 miles on it.

The results weren't good. Here is their quote:
"We normally expect to see high wear in factory fill differential sample, though these levels are a little excessive, even for that. Iron was the dominant metal and shows some serious wear at steel parts. Chrome, iron, and nickel are all alloys in steel, and should read well below average considering the short oil run. Universal averages show normal wear levels after about 29,000 miles oil use. Copper, lead, and tin show poor wearing bronze parts like a bushing. Suggest having this oil changed out if you haven't do so already and resample in 5,000 miles."

You can see the full report on this page of my dealer website:
2006 Cadillac CTS-V Used Oil Analysis Factory Fill Differential Fluid

My recommendation for those that haven't changed out the stock fluid - change it early, whether you chose AMSOIL or another fluid. :cheers:
 

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2004 CTSV
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590 Posts
Results are not unexpected for our differential. It may make sense to change out the differential oil early but the rate of wear of the metal components won't necessarily be reduced by using fresh oil. In fact, if you believe results posted for oil changeouts for the V engines using Mobil 1, the rate of metal loss to the oil is actually at its highest with the fresh oil. It may have something to do with establishing an equilibrium of heavy metals suspended or dissolved in the oil.

So what's the happy median? Change out more frequently and accelerate wear - or less often and risk contamination or degradation of the oil? Either way, if you have a poorly designed, or under-designed, diff I'm not sure the lube changeout interval is the answer.
 

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196 Posts
Well it's obvious to me what the problem is. :bulb: The calcium level is way lower than normal. And everyone knows that calcium builds strong diffs.


oh wait, that's bones....nevermind.
 

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Sedan de Ville, CTS
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4,764 Posts
Thanks for reminder. Just had my Hagen Daas, rum raisin. Best flavor out there. Better than Blue Bell.
 

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2005 CTS-V
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8,363 Posts
All,
I changed out my factory fill diff fluid with AMSOIL Severe Gear Extreme Pressure Synthetic 75w90 a few weeks ago, sampled the stock fluid and submitted it to Blackstone Labs. The fluid had 10,636 miles on it.

The results weren't good. Here is their quote:
"We normally expect to see high wear in factory fill differential sample, though these levels are a little excessive, even for that. Iron was the dominant metal and shows some serious wear at steel parts. Chrome, iron, and nickel are all alloys in steel, and should read well below average considering the short oil run. Universal averages show normal wear levels
after about 29,000 miles oil use. Copper, lead, and tin show poor wearing bronze parts like a bushing. Suggest having this oil changed out if you haven't do so already and resample in 5,000 miles."

You can see the full report on this page of my dealer website:
2006 Cadillac CTS-V Used Oil Analysis Factory Fill Differential Fluid

My recommendation for those that haven't changed out the stock fluid - change it early, whether you chose AMSOIL or another fluid. :cheers:
I recently changed out, and saved, my factory fill at 13,600 miles. I have ordered the oil test kit from Blackstone, but it has not arrived yet. Although, it may be awhile (weeks) I will post my analysis when it arrives.

Based on the appearance of the fluid I drained, I believe it should have been changed it much sooner. Unless and until I see evidence that the rate of contamination has subsided (such as an oil analysis or visual inspection) I intend to change the fluid with each oil change.
 

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2015 BMUU 335i MSport, 2006 STS-V--2005 CTS-V ( traded in)
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Well just judging from my own personal experience, somewhere around 12-14K miles of use the diff starts making the growling sound with low speed turns (reference the TSB) and the car goes back to the dealership to change the fluid and relube it. That's where mine is this morning and one of the things they are scheduled to do to it. I have 31,771 on the car and this will be the third instance of fresh fluid it will see. That is if the dealership doesn't push for a diff replacement.
 

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2005 CTS-V
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8,363 Posts
Well just judging from my own personal experience, somewhere around 12-14K miles of use the diff starts making the growling sound with low speed turns (reference the TSB) and the car goes back to the dealership to change the fluid and relube it. That's where mine is this morning and one of the things they are scheduled to do to it. I have 31,771 on the car and this will be the third instance of fresh fluid it will see. That is if the dealership doesn't push for a diff replacement.
I do not claim to know with certainty, but I think your experience indicates that even if the fluid is capable of adequate lubrication beyond 12-14k the friction coefficient is no longer suitable for the requirements of this particular limited-slip differential. Stated differently, you differential needs a fresh dose of friction modifier at the very least. Naturally, a fresh fill is the best way to reestablish the proper friction coefficient.
 

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2004 CTSV
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I do not claim to know with certainty, but I think your experience indicates that even if the fluid is capable of adequate lubrication beyond 12-14k the friction coefficient is no longer suitable for the requirements of this particular limited-slip differential. Stated differently, you differential needs a fresh dose of friction modifier at the very least. Naturally, a fresh fill is the best way to reestablish the proper friction coefficient.
It would be valuable to see if the lab measured any of these characteristics - although I doubt the friction coefficient is a standard test. I used ATF with friction modifier in a manual tranny on another vehicle and it was shifting fine after 90,000 miles. I changed it simply because I dropped the tranny for a clutch job.
 

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2015 BMUU 335i MSport, 2006 STS-V--2005 CTS-V ( traded in)
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Car is back after the change and all is quiet again. However odds are somewhere between 10-14K and it will be back.
 

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2005 CTS-V
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It would be valuable to see if the lab measured any of these characteristics - although I doubt the friction coefficient is a standard test. I used ATF with friction modifier in a manual tranny on another vehicle and it was shifting fine after 90,000 miles. I changed it simply because I dropped the tranny for a clutch job.
There is a standard test ("chatter test") for the friction coeffecient required by limited slip differentials that is used in testing lubricants. The test, however, is not included in oil analyses because it is a physical rather than a chemical test. Additionally, this friction characteristic is only required by devices making use of internal wet clutches.
 

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2006 CTS-V
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4,042 Posts
Fellas,

If the differential is shreading itself at ~15,000 miles, changing the oil aint gonna do squat.

By the way, mine just started groaning during slow speed turns this week. It's the first time it's made noise since I've owned it and I have 25,000 on the clock. Perhaps it's time for some friction modifier......

 

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2005 CTS-V
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8,363 Posts
If the differential is shreading itself at ~15,000 miles, changing the oil aint gonna do squat.
That is partially true, but we seem to dealing with three different problems.

One is the problem is when the differential comes apart and no one seems to know what causes that. That problem does, however, seem to be limited to 2004 and some 2005 units based on what I read in this forum.

The second problem involves chattering. This condition is the inability of the limited clutches to engage and disengage properly and is apparently caused by the level of friction coeffecient. This is not a part failure, does not represent permanent damage, and can be corrected with a fluid change and/or soaking the clutch packs in friction modifier.

The third problem is noisey operation (the howl). The cause of this problem is neither singular nor clear cut. First, it is somewhat inherent in relative size of the internal gears and the small case. Second, it reportedly gets louder with age, which is not atypical with gear sets. Eventually, the louder howl can be caused by parts wearing to the point where they are longer within operational tolerances. For example bushings or bearings are no longer within serveable limits, the gears have ridging, rippling, pitting, or spalling, the lash/back lash between the ring and pinion are out of tolerance. In other words the wearing parts "wear out." Finally, in the case of the CTS-V differentials there is significant evidence that this third condition can be accelerated by episodes of wheel hop.
 

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2004 CTSV
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590 Posts
But the question still remains - does a lube change every 10,000 miles really increase the overall service life. Mine just started to whine at ~26,000 miles. I haven't changed fluids yet and was waiting to see if I was lucky. Apparently not. If I change the fluid now it may run quiet for a while but the damage is likely done and the tolerances will just continue to increase regardless of the new vs old fluid. This differential was designed to self destruct when placed in the drivetrain with our LS6 or LS2 engines whether you are hard on it or not.
 

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2005 CTS-V
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But the question still remains - does a lube change every 10,000 miles really increase the overall service life. Mine just started to whine at ~26,000 miles. I haven't changed fluids yet and was waiting to see if I was lucky. Apparently not. If I change the fluid now it may run quiet for a while but the damage is likely done and the tolerances will just continue to increase regardless of the new vs old fluid. This differential was designed to self destruct when placed in the drivetrain with our LS6 or LS2 engines whether you are hard on it or not.
Your correct that we do not have conclusive evidence that frequent fluid changes will extend the service lives of THESE differentials. That would presumably require: (1) a number units subjected to frequent changes; (2) another set units operated without frequent changes; and (3) a comparison of resutling service lives or a measurement of accumualted wear and tear.

What we do have, however, is substantial evidence that fluid changes done both early and often seems to coinicide with better results in terms of service life for a number of individuals in this forum. We also know that contaminated fluid accelerates wear on bushings, bearings, and gear sets.

Changing fluid in a unit with 26K may be "too little, too late," but it can't hurt.
 

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2007 CTS-V Thunder Gray; 2004 Cowboy Cadillac (SRT10)
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17,712 Posts
Good write up dm, makes sense to me.

I only have 6K on my diff and I am planning to change the fluid. Some are concerned with warranty but I'm not convinced the GM lubricants are as good as some of the after market versions. Some people are hung up on specs but after hearing that GM realized this diff would not handle the power and they signed it off anyways would make me question whether the fluid meet the specs they outlined for the diff.

It has been my experience in the past that the after market fluids were typically better then the orginal GM versions. GM is a large company and being a large company they will try to cut corners where ever possible. With this being said it wouldn't be a stretch to say they have a chance to put $5 dollar a quart or $10 a quart fluid the bean counters will pick the $5 version. Nothing against GM but they are a large company and the bean counters have more say then any of us on the outside would like. I have heard rumor this is why we have a 6 bolt wheel on the V's for example.

With this said I believe there are better fluids then the GM versions. I have only heard good about the Amsoil but since C66 reps the fluid I would rather hear from someone that doesn't. I don't mean to say I don't trust what you say C66 but since you rep them you might be a little biased.

I am currently planning to put the fluid in my car (Amsoil MaxDiff 75W90) but I sure wish there was more information/tests with this fluid and this rear.

If they won't warranty the diff over fluid then I think they won't anyways because of the power adders I have on the car. Need to find a dealer that believes in customer satisfaction then I should be good to go.
 

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2005 CTS-V
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8,363 Posts
I think we fully vented the brand vs. brand issue in an earlier thread and I am not incliined to revisit that subject now. I do not know whether GM, or any other brand for that matter, actually bottles the fluid they claim to bottle. I think GMs stuff comes from an outside vendor.

I do believe, however, the facts we seem to know at this time fully support frequent fluid changes with whatever brand folks prefer.
 

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2007 CTS-V Thunder Gray; 2004 Cowboy Cadillac (SRT10)
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17,712 Posts
It wasn't my intension to revisit the fluids but just a comment. I'm sure your right, I doubt GM makes the oil themselves. For example, GM doesn't make Silicon wafers (anymore but they used to at Delco in Indiana, Saw it for myself) they buy the Navigation systems.

I agree with your comment about frequent fluid changes however I believe there are better fluids.
 
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