Rear Diff Fluid

[Mbar]

My first track day is coming up. I'm planning on changing the rear diff fluid (per owner's manual's suggestion) after the event.
Does anybody know the GM number for this fluid? OM does not mention it.
Thanks

 

[Quandary]

In my ZL1 I use the below. I would guess it would be the same for the Blackwing;

 

[MatthewAMEL]

Yup. That’s the stuff. The OEM fluid is excellent.

 

[poor-sha]

This is what goes in the 5BW

 

[shbox]

In my ZL1 I use the below. I would guess it would be the same for the Blackwing;

Same stuff my old ATS used.

 

[Daijoubu]

This is what goes in the 5BW
View attachment 8450

I was wondering if it was the GL-5, like the SS Sedan used. I didn't want to comment because I didn't know for sure, but if this differential needs the GL-5 then putting in the LS fluid will not be good. If the clutch packs require GL-5 and you put in the LS fluid, be ready for a one tire fire, just like what would happen in the SS.

What is weird is when I needed the fluid for my SS, the Cadillac dealer is the only place I could find it in stock. I'm still not sure what other Cadillacs used it.

 

[Mbar]

Now we have a problem….

 

[Quandary]

This is interesting. Have you called the dealer to ask them?

 

[Mbar]

This is interesting. Have you called the dealer to ask them?

I called. Dealer did not know. They said somebody from service needs to dig into the service manual, as the car is too new and it doesn’t show under the parts list. They had several options which 2 of them listed above. Didn’t know which one is the correct item.

 

[Quandary]

Well that's reassuring.......

 

[Daijoubu]

@poor-sha , has the FSM, I think? Is that where you got the info?

 

[Mbar]

The dealer sent me this doc from the service manual. I still don’t feel warm and fuzzy about the correct fluid…

 

[Quandary]

That is the data for a CT4. While it is possible I think it unlikely that the CT5-V Blackwing has the same rear diff as a CT4. I would think as it is the same power train as the ZL1 that it would be far more likely that the diff in the ZL1 and the Blackwing would be the same.

 

[Daijoubu]

19418501 is the GL-5 that is referenced above. The rear ends may not be the exact same in both cars, but the main point to consider is the material that the diff clutch packs use. That material needs a very specific lubricant in order to work as designed. I had a SS sedan at one time, and everyone just assumed it used a Camaro drive train, which is mostly true. However, it used different clutch packs and those that put in the LS oil experienced basically an open differential since the friction was not right. I wouldn't go assuming on the diff fluid with these cars.

 

[poor-sha]

I confirmed with @Mirza Grebovic I had the right fluid for the 5BW.

That was after I contacted him in a panic because the car was making a horrible screeching noise after I replaced the diff fluid. Issue turned out to be a stone between the rotor and backing plate. Such a gracious guy with his time and assistance.

 

[poor-sha]

I guess I should ask, which BW are we talking about?

 

[Mcard23]

Went to change my diff fluid in preparation for Road America in a couple weeks....what size Torx did you use for the drain/fill plugs? Got under the car expecting it to be the same as my 6 gen camaro and realized I didn't have the right tools lol

 

[MatthewAMEL]

Went to change my diff fluid in preparation for Road America in a couple weeks....what size Torx did you use for the drain/fill plugs? Got under the car expecting it to be the same as my 6 gen camaro and realized I didn't have the right tools lol

It's a Torx? On the 'vette and Camaro, it's just the 1/2" end.

 

[RDATLTE]

Went to change my diff fluid in preparation for Road America in a couple weeks....what size Torx did you use for the drain/fill plugs? Got under the car expecting it to be the same as my 6 gen camaro and realized I didn't have the right tools lol

Damn, that's a pretty reasonable expectation.

 

[Mcard23]

It's a Torx? On the 'vette and Camaro, it's just the 1/2" end.

View attachment 8562

Looks like it to me lol. Very different looking unit than my 6gen