1999C5JSS

Hi guys I got 2 bottles of AC Delco rear diff fluid from GM
part number in Canada 89021678

I notice from searching on here some say that this fluid "does" have LS additive already mixed in. this info is not correct and wanted to let others know

if you run the part number above you must buy the additive

here is email from gm/ac delco

Thank you for your inquiry. We have consulted with our ACDelco TAC team and they have confirmed that the ACDelco Rear Axle Lubricant/PN 89021678 is a synthetic gear lubricant. It does not contain limited slip additive. To inquire further about ACDelco products including fluids and lubricants, we suggest that you contact an ACDelco distributor.

jhopper408

Wow! And I'm getting ready to change all of my fluids at a Chevy dealer. Will they know the correct fluids?

1999C5JSS

I don't think they do. parts guy at gm search my car based on Vin and said I just need rear diff fluid part number 89021678. I even asked him about additive and he said does not come up as needed.

thats when I started researching and finally just contacted AC DELCO.

Anthraxmm

I just put the Mobil 1 synthetic gear oil with the limited slip already mixed in it says LS right on the bottle.

Thanks for sharing the info, I wonder how many people have used this with out the additive.

jhopper408

Yeah I'll make sure it's the correct fluid. Thanks guys!

garline14

Thanks for sharing the info!
I recently changed my Rear Diff fluid out and was deciding between AC Delco and Amsoil. I went with Amsoil after reading many great reviews and it has the additive already mixed into it. Did some figure 8's and all is well

jackthelad

Repair manual clearly says to use limited slip additive. Note however, that the manual was written before "LS" rated lubes were available.

When I did "front to back" oil changes recently, I used Mobil 1 LS - no issues as far as I can tell.

IH8FORD

That is not correct fluid for your car. 88862625 dexron ls gear oil is correct which has the additive. That's the Canadian part number.

C66 Racing

AMSOIL Severe Gear Extreme Pressure Synthetic 75w90 (Product Code SVGQT)

For those that would like to try the aftermarket option, more than happy to get AMSOIL products for forum members at dealer wholesale pricing, about 25% below retail, via the AMSOIL Preferred Customer Program. Drop me a PM if interested.

craig04c5

I have a 4:10 rear supplied by DTE. They specify Red Line synthetic which has LS but they also specify to add 1oz of Red Line additive to each quart.

jackthelad

For the sake of completeness, this is what the Service Manual for the C5 originally said:

Rear axle lubricant GM P/N 12345977 or equivalent (1.6 L, 1.7 Qt)

Limited slip additive GM P/N 1052358 or equivalemt approx. 100ml or 3.4 ozs.

As I posted earlier, LS lubes were not available back then, so you had to use the additive - these days an LS 75/90 will do the job..

1999C5JSS

12345977 was old non synthetic fluid which was officially replaced by 89021677(89021678cnd) which is synthetic.

I was not told from GM that the LS series was the new part for the c5. so this is why I didn't use it.

I am sure if it was approved to be c5 ok it would be the new part number on the c5 parts catalog.

if you can contact gm or ac delco and see what they say that would be handy info to share.

IH8FORD

88862625 dexron ls gear oil. Is the current fluid listed on service information which is what is used by dealerships for repairs. That is the Canadian part number.

1999C5JSS

just so we are clear you are saying you have the proof from GM parts catalog etc for a c5 generation cars listing that it is the fluid for us to use?

reason why I ask is because GM told me my listed part number is correct.

I made this posting on here to help others in future get the facts.

please confirm or share you findings stating gm calling your part number as new fluid to use

thanks for all the help guys.

please lets keep this posting talking about GM fluids not amsoil etc

IH8FORD

That is directly off service info

1999C5JSS

great info thats what we needed on here thank you.

looks like tomorrow I will call dealers to set some facts out to them and ask why they shared my info.

IH8FORD

Don't get me wrong the other fluids with a additive will work. The ls fluid they came out with due to the bad shudder in the c6s.