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2007 CTS-V Thunder Gray; 2004 Cowboy Cadillac (SRT10)
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Discussion Starter #1
Bad title, meant to ask what is the proper oil...

I just came back from goodies and they didn't carry the RP max diff fluid. They were a Amsoil dealer so I bought the Severe Duty 75W90W.

I came back to the office and read the bottle and it said it will work with "most" limited slip rear ends and if you have any chatter add the additive.

I have checked and AmsOil has a limited slip additive and I was thinking since I have AmsOil I should use their additive but I don't know.

The question is should I use the GM additive or the AmsOil additive?

This gear oil is not cheap at $18 a quart but I will do almost anything to try and keep this rear end in one piece.

I am going to put the RP Syncromax in the tranny, new flywheel, Headers... I am going to change the oil in the diff after I get a couple of miles on the above mod's. I am leaning twoard just putting the AmsOil additive in but I figured it would be good to see what experience others on this forum have had.
 

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2005 CTS-V
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If your going to use Amsoil Gear oil I suppose you should also use Amsoil's additive. The GM gear oil, which is the only one that meets the required GM 9986115 specification, already contains friction modifiers and yet GM still calls for an additional dose of friction modifier in the OE recipe. So it follow that non-GM gear oils would also need a "second dose."

BTW the 9986115 specification requires, among other things, a higher level of temperature stability that the GL-5 specification that most gear oils do meet.
 

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2007 CTS-V Thunder Gray; 2004 Cowboy Cadillac (SRT10)
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Discussion Starter #3
I found this on AmsOil's web site:
___________________________________________
LUBRICANTS & FLUIDS
Engine Oil
Grade 1......API*[1]
Series 2000 Synthetic 0W-30 Motor Oil
SAE 5W-30 Synthetic Motor Oil
SAE 5W-30 XL Synthetic Motor Oil
All Temps......5W-30[2]
Manual Transmission,Tremec 6-Speed.....GLS[3]

Controlled Slip Differential, Rear .....GL-5*[4][5]
75W-90
Severe Gear 75W-90

[4.] Synthetic lubricant, GM part no. 12378261, specification
No. 9986115.
[5.] With complete drain/refill add 4 oz part no. 1052358
_________________________________________________

Thanks for supplying the Part number and it looks like the oil is a replacement for the GM oil, it appears they meet the GM specification according to the blurb above.

It appears the additive is required as with the GM oil. The part number they give is for the GM additive and not their own, interesting...

Thanks for your help darkman.

Combination I will go with as of right now is AmsOil/GM Additive unless I hear a reason not to.

please keep any other comments/experiences coming, thank you.
 

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2005 CTS-V
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I found this on AmsOil's web site:
___________________________________________
LUBRICANTS & FLUIDS
Engine Oil
Grade 1......API*[1]
Series 2000 Synthetic 0W-30 Motor Oil
SAE 5W-30 Synthetic Motor Oil
SAE 5W-30 XL Synthetic Motor Oil
All Temps......5W-30[2]
Manual Transmission,Tremec 6-Speed.....GLS[3]

Controlled Slip Differential, Rear .....GL-5*[4][5]
75W-90
Severe Gear 75W-90

[4.] Synthetic lubricant, GM part no. 12378261, specification
No. 9986115.
[5.] With complete drain/refill add 4 oz part no. 1052358
_________________________________________________

Thanks for supplying the Part number and it looks like the oil is a replacement for the GM oil, it appears they meet the GM specification according to the blurb above.

It appears the additive is required as with the GM oil. The part number they give is for the GM additive and not their own, interesting...

Thanks for your help darkman.

Combination I will go with as of right now is AmsOil/GM Additive unless I hear a reason not to.

please keep any other comments/experiences coming, thank you.
Thanks for the info on Amsoil - the last time I looked I could not find anyone (including Amsoil) claiming to meet the GM 9986115 spec, but now it seems there is. On which Amsoil website did you find that info?
 

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2005 CTS-V
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Since my post above, I have found the Amsoil reference on its website. I think it is ambigous and have, therefore sent Amsoil an e-mail inquiry that simply asks whether their Severe Gear 75W-90 is certified under, or failing that, at least meets the GM 9986115 specification. I will report their answer.
 

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2007 CTS-V Thunder Gray; 2004 Cowboy Cadillac (SRT10)
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Discussion Starter #7
It wasn't quite clear if it meets the sepc or not but the way they wrote it it "kind of" implies it. Better to confirm so thank you for sending an email to find out.
 

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I may not receive an answer today, and I will be out most of tomorrow. If you need to finish up your car, I cannot imagine the Amsoil / GM additive recipe doing any harm. I just wouldn't pull into a dealership for warranty work on a broken diff with non-spec juice in the thing.
 

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order rp. Have it sent to you if you must. Change the fluid early and often if you hope to keep it quiet.
 

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Discussion Starter #11
I tried to buy the RP but Goodies didn't carrry it. They tried to push the Amsoil ATF but I bought the RP Syncromax.

I don't plan to put the fluid in for at least another week or so. I just wanted to get the trans fluid changed before I installed the tranny. Much eaiser to add the fluid while the transmission is out of the car.

Thanks all for the help so far.
 

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2005 CTS-V
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RP has the goop in it already...a nice feature.


F
If you use Royal Purple you will still need an additive because you need TWO doses of the goop to match the OE recipe in terms of friction modifier. Royal Purple, as far as I have been able to determine does not meet the GM Specification 9986115 in terms of thermal durability above and beyond the API GL-5 threshold.
 

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crushing Vs with my Wurm
2013 GT500 - 700+ HP
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If you use Royal Purple you will still need an additive because you need TWO doses of the goop to match the OE recipe in terms of friction modifier. Royal Purple, as far as I have been able to determine does not meet the GM Specification 9986115 in terms of thermal durability above and beyond the API GL-5 threshold.
My vehicle has a locking differential. Do I need to add additional friction modifiers when using your Max-Gear®?

No. All viscosities of Max-Gear® are formulated with hypoid friction modifiers necessary for use in clutch or cone type differentials. No additional additives are necessary.


I dont have a Getrag rear, so my application is different.




F
 

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My vehicle has a locking differential. Do I need to add additional friction modifiers when using your Max-Gear®?

No. All viscosities of Max-Gear® are formulated with hypoid friction modifiers necessary for use in clutch or cone type differentials. No additional additives are necessary.

I dont have a Getrag rear, so my application is different.


F
Okay. My remarks were based on the requirements of the initiator of this thread who asked about a stock CTS-V differential because I interpreted your observation as being applicable to his vehicle. Apparently it was not. My mistake.
 

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Rob,
The Severe Gear 75w90 is the correct AMSOIL gear lube for the CTS-V. It comes with friction modifier already mixed in and adding additional, whether you chose to use GMs or AMSOIL's, isn't required unless your differential chatters.

I have been using that exact fluid in my 02 Corvette Z06 on the track for years and haven't had one diff failure (other than a failed left axle seal which is a common Z06 problem, and in that failure the diff held up and I won the race despite losing a quart of the two quarts in the diff). This fluid is also very highly regarded on the Corvette Forums. I can PM you a few recent links of guys who have given up on the TSBs out on the C6 diff noise, switched to the Severe Gear 75w90 (with one bottle of the AMSOIL additive) and had the noise go away and stay away.

I put the same fluid, without additive, in my 06 CTS-V a few weeks ago. No problems, no chatter.

As an FYI, that is also the fluid AMSOIL recommends for the CTS-V per their AMSOIL Online Product Application Guide, and thus as you are using it per their recommendation, you are covered per both GMs factory warranty (which can't be voided for using aftermarket fluids) and the AMSOIL Corporate Warranty.

As an FYI, that price is ridiculous and is about a 50% mark-up over AMSOIL's suggested retail price. I could have gotten you the same fluid for about half what they charged you.
 

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As an FYI, that is also the fluid AMSOIL recommends for the CTS-V per their AMSOIL Online Product Application Guide, and thus as you are using it per their recommendation, you are covered per both GMs factory warranty (which can't be voided for using aftermarket fluids) and the AMSOIL Corporate Warranty.
I agree that GMs factory warranty cannot be voided for using aftermarket fluids, IF, AND ONLY IF, the aftermarket fluid in question meets the specifications set forth by GM. That is the reason it is okay to use any motor oil that meets the GM4718M specification, which includes many different brands.

However, I have received a response from Amsoil and it does not claim that its Gear OIl meets GMs Specification 9986115, which calls for a threshold of thermal durabilty higher than that particular to the API GL-5 standard. Thus, GM can legally void the warranty on any differential that contains Amsoil or any other gear that does not carry that specification.

I am not saying that any particular GM dealer would actually exercise that opiton, because I do not know that for a fact.

Further, I am not saying that using Amsoil or any other gear oil that cannot pass the GM 9986115 standard for thermal durability will necessarily result in damage because I do not have any direct evidence of that either.

Personally, I am going to use the GM gear oil because: (1) I do believe that passing the GM 9986115 specification indicates a fluid with superior themal durability; (2) I see no reason to risk the GM warranty in order to use a non-spec. fluid.
 

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Darkman has some good info on the GM spec's for the rear gear oil. Do you know if they specify the same fluid for the standard CTS rears? Seems like they should have specified a more severe service rated fluid for the V application.

I agree with you on not wanting to jeapordize the warrantee by using non-factory spec fluids. On the flip side, you sure can't say that using the factory fluid prevents all problems with the differential. Thats not to say that the gear oil is causing the problems, but it sure as heck isn't preventing them either. Given all the issues with this diff, and Cadillac's pitifull response, my confidence that GM has selected the optimum gear oil spec is pretty damn low.

I'm on diff number 5 with about 5K on it, and it has begun to whine pretty loudly at part throttle between 45 and 60 mph, and now has a nasty whine on coast down (hadn't had that on previous rears). No problems yet with lsd clutch grabing on slow turns, but expect that soon. This diff has pretty much been babied. No track use, no clutch dumps, maybe a handful of strong 1-2, 2-3 shifts.

I'll be trying an aftermarket fluid to see if I can quiet diff number 5 a bit, and from the start on number 6 (probably in another month or so). The extended warrantee is great, but I'm really tired of the dealer visits and worrying about if/when it is going to die.
 

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I do not know what GM specifies for the CTS. I agree that GM's fluids do not seem to be preventing the failures. I just want the dealer/GM to pay for those failures instead of me, hence the concern over the fluid meeting warranty requirements. In any other vehicle (including GMs) I would run whatever I wanted (e.g. Amsoil) because thermal durabiliy is not uusally an issue and differential failures are generally considered rare.
 

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Understand your points Darkman, but disagree a little. Factory warranties specify that damage caused by the use of aftermarket products (including lubricants) won't be covered. For example, my 02 Z06 owner's manual warranty (which I had handy) states "Damage caused by failure to follow the recommended maintenance schedule intervals and/or failure to use or maintain fluids, fuel, lubricants, or refrigerants recommended in the owner's manual is not covered." The key point is "damage caused by...". The damage to your diff isn't likely to be caused by any aftermarket fluid, no matter whether it meets the GM Standards or not. All that said, many won't want to deal with the hassle of arguing this point with GM and will chose the factory fluids.

Personally, I feel that with a Group IV PAO basestock, the AMSOIL Severe Gear is going to be more thermally stable than whatever GM is using. When I lost my left axle seal in my diff at about lap 6 of a 20 lap race in early 2005, I lost about a quart of diff fluid during the race. The diff held up and I won the race. As a precaution, I had my diff rebuilt after the race and the race shop estimated my diff temp at over 400F (it melted the plastic speed sensor it got so hot). Based on my experience, I'll stick with the aftermarket fluid and rely on AMSOIL's corporate warranty if GM balks.

And, I agree with Mark that the factory fluids aren't getting the job done. When I submitted my diff sample (10k miles on the original factory fluid) to Blackstone for analysis a few weeks ago, here was there response:

“BRADFORD: 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.”

I haven't found time to post the full report to my website yet, but I plan on getting to it this weekend and I'll post a new thread on the topic.
:cheers:
 
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