View Full Version : Rear Diff Fluid

11-07-07, 11:13 PM
My last rear diff was put in about a 1,000 miles ago and it is starting to whine again and this time its louder. I am going to have the fluid changed and was wandering if there is anything that is recommended other than the GM products.

11-08-07, 05:00 AM
Dyno-Tech Engineering, the people who built the differential for my C5, are big proponents of Redline diff fluid. They even have a Limited Slip additive. I have been using the Redline diff fluid since 2003 in my C5. When it is time to service the diff in my V, I will use Redline in it, also.

11-08-07, 06:29 AM
I haven't used much other than what we have in the shop which is the GM stuff.
I know GM is coming out with a new fluid sometime this month to deal with the clutch chatter on turns for the CTS and XLR with G80.
I have no idea who they are getting it from or what is in it.
The guy I have been talking to about it said it already has the friction modifier "built in" but as I mentioned it isn't out yet.

The only other thing I do know is that a different guy at TAC suggested I use a Mobil branded lube and adding the friction modifier for an issue with the XLR.
I am sure other guys have tried different things with degrees of success, hopefully they will chime in.

11-08-07, 07:39 AM
There are a number of earlier threads on this subject.

I use the GM fluid (and its companion additive) because it is the only fluid I have found that meets, or even claims to meet, the GM Specification 9986115 required by the warranty. The GM 9986115 Specification requires the fluid to survive additional high temperature tests not included in the otherwise applicable API GL-5 standard.

11-08-07, 12:37 PM
I am not tracking the car and by no means am I an expert.

With that out of the way, I am using the AmsOil Fluid that they recommend and the diff is quiet as a church mouse at 10K.

Please do more research before using anything else in the rear diff as it could effect the warranty if you have problems in the future.

I hope ewill reads this and chimes in. If you see another fluid in the rear other then the GM fluid would you deny a claim for warranty based on this alone?

11-09-07, 06:50 PM
As mentioned I like to see fluids that meet the GM specs listed in the owner's manual.
Unless the fluid has some coloration that would distinguish it from GM stuff I really have no way to know what is in it.
If it came out looking like something besides what I expect then I might call upon management to make the final call. I can't really tell if it is the wrong lube by looking at it.
When I do warranty replacements I drain the fluid, which leaves only a trace. From there it is up to GM to decide whether or not I knew what I was doing when I fixed it. If they call back the part and find something else in there they could charge the repair back to the dealership and James might not like that if I made the call.

It does have to meet GL-5 lubricant specs, I think the GM spec number is listed above.
The bottle should be clearly labeled on the back (fine print like) as to what specs it is designed to meet or exceed.

11-09-07, 07:12 PM
Hi ewill,

found this on their web site. Talk is cheap but according to the Web page it is GL-5 compliant. Wonder how I could find out if this is true?

BTW, What color is the Fluid supposed to be? When I drained mine at 6K there was a bunch of sludge in it and the color was close to a gray. I kept a sample of what came out just because it did have me a bit worried. I'm guessing it was the clutch packs and I'm wondering if this material coming off the clutch packs is causing some problem. I will be sending an email to Lynn to find out how they built up the rear for the VR. (They used mobil 1 of course, but they had a special blend)

2007 CADILLAC CTS 6.0L 8-cyl Engine Code U
Standard Differential, Rear .....GL-5[5] (CTS)
All Temps......75W-90
Severe Gear 75W-90
SAE 75W-90 Synthetic Gear Lube
Severe Gear 75W-110
Controlled Slip Differential, Rear .....GL-5*[5][6] (V)
All Temps......75W-90
Severe Gear 75W-90

1. Must use synthetic engine oil.
2. Must use synthetic engine oil.
3. Gm recommends part no (USA 88861800) Canada (88861801)
or equivalant for manual transmission, transfer
case applications.
4. Use GM part no. 89021806 or equivalent.
5. Synthetic lubricant, GM part no. 12378261, specification
No. 9986115.
6. With complete drain/refill add 4 oz part no. 1052358

Differential, Rear..........2.7 pints


LInk for the above information:
Once you click on the link then you will need to enter the year (Mine is a 2007) then select the car.

11-09-07, 07:45 PM
I believe most off the shelf, multi-weight gears oils meet the API GL-5 specifications, particularly the synthetics.

The GM fluid does have a distinct odor. As already pointed out, the GM fluid is relatively clear when new and in used condition it would be difficult to spot the GM fluid as opposed to others unless it had obvious coloration (such as purple). Thus, unless the dealership retains a sample you are left artguing, after the fact, about odor which does not seem likely.

11-09-07, 09:29 PM
Whatever gets drained out at the dealership will be grey/black.......no way is any dealership going to deny warranty based on color.......It's always the same.....I've changed my diff fluid a number of times with different brands of gear lube.....and it's always the same color.

11-10-07, 09:07 AM
Yes it can get pretty dark, most of what I see come out is really dark.
I don't save samples of the fluid, but some is left in the diff as you can't really drain it all.
If GM wanted to split hairs it might be an issue, however they could only come back after us, not you guys, to pay for the repair.
I think they have enough of them laying around to worry about that they won't study fluid samples from everyone we send back.

I usually recommend whatever the manual recommends. I don't have any non-GM specific recommendations.
To be frank, when I condemn a rear end I don't really check the fluid at all.
I base it on how loud it is or how shattered the case is ;)

11-10-07, 06:16 PM
I'm switsching all my cars/trucks to Torco synthetic with their limited slip friction modifier type G for the general ( they list a type F for other makes) just because I like what Torco has to offer as a lube company. Both their history and current technology from a small family owned business is the kind of people I like to deal with. And for all you full race guys try that SAE 250:histeric::histeric: