Proper Gear oil for the Rear

[C66 Racing]

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.

[darkman]

Originally Posted by C66 Racing

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.

[markh]

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.

[darkman]

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.

[C66 Racing]

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.

[CTSV_Rob]

This is all great information and at this point I'm not sure what to do. The one thing I will not do is buy this fluid from Goodies again, thought it was a bit too much but I have never run the Amsoil before.

With all of the horror sories I have heard so far about these diff's I would like to try anything to help them along. Considering they have a reputation of dying I would have to agree that the GM oil is as good as it could be. If the rear ends were solid I would probably stick with the GM fluid.

I am not a chemical engineer but maybe the properties of the fluid are such that the factory oil does not "lubricate" as well as the higher end after market conterparts. So far I have heard that the people that have switched to an aftermarket fluid their diff's are holding strong and they aren't your typical "drive to work" type of driver. They know how to push these cars to their limit but it could also be that they now how to apply the power to keep the rear end's in one piece.

The corvette story is compeling though. From what I have read so far it is conveincing that this fluid will help the diff in the long run however I agree with Darkman about preserving the warranty.

I am going to contact my local dealer that will be changing the diff under warranty and see what their opinion is. May get it in writing if they say it ok to use this fluid. Do you think they would send it in to be analyzed if the diff fails? I would guess they wouldn't even know about the fluid especially if it grenade's and the fluid spills all over the road.

Florian, Not very nice rubbing our noses in the fact that you have a solid rear!

Really like my 07 and I want to make it run to it's full potential. In the end I may end up doing what Florian did if there is no other option by the time I'm ready. I wish someone would make a drop in replacement but I doubt that will happen for such a limited production car.

Ultimate goal is 600 RWHP but this is a few years off and much planning.

Thank you CaliCadi, C66 Racing, Darkman, MarkH, Florian (I think)...

[Feffman]

If one uses the RP, what is the RP part number or RP product name and do we need to add a friction modifier?

Feff

[nikon]

I've used the amsoil and the RP, nothing more added and it didn't chatter....On my current diff (third) with factory fluid and factory additive, the diff chatters....so to me...I say if your in warranty, let it make noise and keep getting it replaced...eventually they'll do something about it.

[C66 Racing]

Originally Posted by Feffman

If one uses the RP, what is the RP part number or RP product name and do we need to add a friction modifier?

Feff

Feff,
The appropriate RP product is the 75w90 Max Gear Synthetic Gear Oil. RP advertises that this gear oil comes with friction modifiers already in it and that no extra additives are necessary. Never used it myself though, so can't comment directly.

[Feffman]

After the great content out here regarding rear ends (the V that is!) I had the dealer change the differential fluid with the oil change this morning. Seems using GM's fluids to avoid any potential warranty issues was the prudent course of action. Think I'll make this part of maintenance about evrey 3rd oil change.

Happy Motoring!

Feff
www.MVPTrackTime.com

[Florian]

Originally Posted by CTSV_Rob

Florian, Not very nice rubbing our noses in the fact that you have a solid rear!

Ultimate goal is 600 RWHP but this is a few years off and much planning.

Thank you (sic) Florian (I think)...

Not rubbing any noses....I wasnt able to drive my V for 6 months....talk about Jonesing!!!! Now, no issues. Just gotta pay to play....same as with any other car. HP = $$ (in one form or another....)


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[Florian]

Originally Posted by Feffman

If one uses the RP, what is the RP part number or RP product name and do we need to add a friction modifier?

Feff

MaxGear 75W90. No modifier needed. Ive used it for 2 years....



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[CTSV_Rob]

Originally Posted by Florian

MaxGear 75W90. No modifier needed. Ive used it for 2 years....

Hey Florian,

6 month's without the V, that would definitely suck. The last time was 2 weeks and that was bad enough. You paid your Dues and now have a rear that should be able to take anything that LS6 can throw at it. I appreciate your comments but I have to say I am a bit jealous of your setup.

Happy with the Gear oil so far? Has it made a difference? Would you recommend it?

I have already purchased the MaxGear but have not put it in yet. I have a problem with the BB exhaust setup that I'm trying to work out but getting some resistance.

[Florian]

Originally Posted by CTSV_Rob

Hey Florian,


Happy with the Gear oil so far? Has it made a difference? Would you recommend it?

I have already purchased the MaxGear but have not put it in yet. I have a problem with the BB exhaust setup that I'm trying to work out but getting some resistance.

Ive never had one single issue with the MaxGear....I swear by it. As far as making a difference, I dont know, although my rear never failed with the RP in it, and it did make it a bit less noisy. Youre gonna need an oil gun to get it in your diff though. They can be found at just about any auto parts store. All my go-fast toys have RP in em.....Im using Syncromax in the tranny BTW. I have no stock in RP, just a satisfied user.


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[Silver Dollar]