diff additive

[First Class Motoring]

hey guys,just got my car back from the dealer from installing a new diff.they did not put the additive in said it had a synthetic gear lube.should i put the additve in or is it ok with synthetic lube?thanks

[ronr]

Originally Posted by caddiyesso

hey guys,just got my car back from the dealer from installing a new diff.they did not put the additive in said it had a synthetic gear lube.should i put the additve in or is it ok with synthetic lube?thanks

You do need the additive (even with GM synthetic lube)
________________
Ron,

I am the service engineer for the CTS/CTS-V rear drive modules (RDM). I consulted with Sumie Thaker, the design engineer for CTS/CTS-V rear drive
modules to make sure that I provided the correct information to you.
Both the CTS and the CTS-V use synthetic fluid (GM p/n 12378261). All '04 - '07 CTS-Vs are equipped with limited slip RDMs so they all require the additive (GM p/n 1052358) in the required amount specified in the service information.
There is no external identifier for a limited slip RDM. The RPO for limited slip is "G80" and can be found on the SPID (Service Parts Identification) label. Since all Vs are equipped with limited slip, your vehicle requires the synthetic fluid and the proper amount of limited slip additive.
I pasted the service information document "Lubrication Specifications" for the '04 - '06 CTS/CTS-V at the bottom of this e-mail for your reference.

Please give me a call if you have any questions

Steve Underwood
Service Engineer - Driveline/Axle - Sigma, Kappa, Theta/Epsilon & Midsize Truck
MC: 480-210-1B2
VEC-Podium - Cube 1M12-23
30001 Van Dyke, Warren, MI 48090
Ph. (586) 575-4564
Fax. (586) 575-4000
e-mail - steve.underwood@gm.com

[First Class Motoring]

thanks.

[austin]

>hey guys,just got my car back from the dealer from installing a new diff.they did not put the additive in said it had a synthetic gear lube.should i put the additve in or is it ok with synthetic lube?thanks


Hooooold on a minute... I just asked this very same question a week ago as well. The dealer said the same thing to me about the additive not needed due to synthetic fluid. Now i'm not too sure what is going on... Why would different dealers be telling the exact same story.. This needs further investigating.. Maybe the newer diffs are shipping with just the additive in them already??? Or GM's fluid now contains friction modifiers like other diff. fluid from other company's... And now the additive is not needed.

Here is the part number for the fluid they used; #89021677

[dvandentop]

unless they put royal purple in which alreayd has the diff additive in but i doubt they did

[rand49er]

Austin, that's the same lube they put in mine last July PLUS they put the above mentioned additive (PN 1052358) in. I have what I consider to be a superior dealer. Don't trust yours.

You NEED that additive!

[First Class Motoring]

does royal purple rilly have the additive in it?

[dvandentop]

i had it in my z06 for many miles and never had issues after i swapped to royal purple

[ronr]

89021677 replaced 12378261 and it DOES require the additive just like the other.

The root cause of the confusion at the dealers is (or should be) whether your car has a limited slip differential.

The other part of the email I received contained the following:
______________
Sumie,

The following e-mail has a couple of questions concerning '04 - '06 CTS-V RDM lubricant. To summarize the questions:
1. Do all CTS-Vs have limited slip RDMs, and if so, do they have the G80 RPO or is the limited slip RDM included in a CTS-V specific RPO? (I'm looking for an easy way to tell the dealer to find out if the RDM is an open or limited slip) - All '04 - '07 CTS-V (GMX-320 V) have LSD. G80 is the RPO for LSD.

2. It looks like both the open and the limited slip RDMs use synthetic lubricant, is that correct? - Both open and LSD uses synthetic Lubricant.
3. Does the limited slip RDM require an additive? - Yes. We add additive to synthetic lube for LSD applications.

4. Is there an external identifier for the limited slip RDM? - There is no external identifier for LSD. From VIN they can identify if axle has G80 - LSD.


I've attached a copy of the service information for lubricant specifications for '04 - '06 CTS (including V). Please take a look at it to make sure it is correct.

Please give me a call or send me a note back and I will respond to the e-mail.

Thanks,

Steve
__________
In the service documentation that was sent to me it clearly states that LSD's need the additive. The argument I got into with my dealer was that the mechanic couldn't confirm the car had an LSD (I'm thinking he was on LSD!) This is why the answer to my question contained the RPO code information.

[Lindsay Cadillac]

Here's the information from the service manual... It needs the additive...

Unfortunately you can't use the G80 option code to determine if the V has a limited slip differential, it's not on the SPID label. The problem arises when a dealer can't get their head out of their but to see that the car has a limited slip even though it doesn't have the G80 code...

[Lindsay Cadillac]

Here's the actual fluid change procedure from the service manual... It specifically mentions using the additive with a limited slip differential...



I can't believe this still comes up...

[ronr]

Originally Posted by Lindsay Cadillac

Here's the information from the service manual... It needs the additive...

Unfortunately you can't use the G80 option code to determine if the V has a limited slip differential, it's not on the SPID label. The problem arises when a dealer can't get their head out of their but to see that the car has a limited slip even though it doesn't have the G80 code...

You're right on. I too found the G80 wasn't there but I thought they got that fixed with the '06 and beyond cars. The mechanic at my dealership was on a mission to prove me wrong about this. He already had egg on his face since he first filled my new diff with non-synthetic so I had one up on him re: the synthetic and he was bound and determined to even the score on the additive. Good thing my service writer was in my corner and just insisted on the mechanic adding the additive.

[First Class Motoring]

so,does anyone know if royal purple has the additive in it?

[Flyboy]

Yes....I use RP......and it HAS the additive blended in already. (I spoke with one of the techs there)......very nice people BTW.

[First Class Motoring]

thanks.