Diff fluid recommendations
 

Howdy all...not to beat a dead horse...

2018 SS M6. What is the preference for the rear diff fluid? Does everyone stick with the AC Delco (GM) brand which has the limited slip additive included or do you go with a different brand?

I have used Mobil 1 synthetic rear diff fluid (and a separate additive for the limited slip) in my '15GMC with no issues.

I doubt if I will ever track the car but do use it at times as it was intended for (hard launch at start up, gitty up and go on the turnpike)...

What about the transmission (six speed)? Is it recommended to change that fluid out as well?

Car is almost at 400 miles and quickly piling up :). LOVE this car!!!!

Just curious to see what everyone has used in the past.

Thanks all.

Lee

consensus is to use the AC Delco 75w-90 with limited slip, AC 10-4034

Thanks Mike!

I would add Motul Gear 300 LS (Limited Slip) to the recommendations.

I guess that if a company like LG Motorsports (among other high-class / reputed speed shops) uses it, then they certainly know to appreciate its high performance.

The AC-Delco stuff (which is actually produced by Petro Canada) is decent stuff by all means, but cannot be categorized in the "High Performance / Racing / Endurance" category.
For the average/daily driven street, it is indeed perfectly fine and safe to use.

Here some background / reading material / References:

https://www.lgmotorsports.com/access...-ls-75w90.html

https://www.motul.com/us/en-US/produ...r-300-ls-75w90

AC Delco, Dexron LS (GM's OE) 10-4034
https://lubricants.petro-canada.com/...uctline/dexron

Just had my pumpkin oil changed, second time- around 4200 miles on it.
Last couple days, I noticed on pulling off; at the end of the drive, it growls when I turn out on the road. So far, it quits within 1/4 mile or so.
The shop had run out of 75w-90 oil, and went up the street and bought some at a place you couldn't pay me to get anything.

Wonder if they sold the shop a bunch of slop that doesn't work well with limited slip ???

Get the AC Delco that has the additive already in it. I had diff groan when cold after only 1500miles. I changed with Synthetic Mobil 1 75-90, groan got worse. Changed again with Valvoline Synthetic, no better. I ordered AC Delco #88862624 and changed it again and the groan was much better. It took about 1500 miles, but now it's completely gone. Car is at 5k miles now. I think a lot of it is the differentials breaking in because they are setup really tight and need the fluid changed early in life. I honestly would change it with the first oil change in the 500-1500mile range and no later.

I changed mine (dirty) around 1500, then last week at ~4200. Groaning manifested itself this last week, so got it changed again, now at 4442. Took it into a couple parking lots, and went around in circles CW, & CCW---parked it.
If it's gonna do it, will happen when stone cold, later tonite, or morning.
(crossing fingers)
Doesn't work, will get the delco stuff.

+1

Some people are going to call me crazy but I swapped mine out for Redline 75w140 and all the groaning went away. The other benefit was better clutch engagement (car was way smoother in tight turns). I did track the car regularly which is why I went with 140 weight but even in street driving there was no noticeable downside here in Colorado winters. I am a huge fan of Redline fluids in general, and they do make a 75w90 but I just wanted to share my experience.

Added CRC-- diff. friction modifier, 2 oz to the rear end, without anything else.
Waited about 15 hours to be sure it was cold, and so far today, no issues. Hope I'm done with that chore.
Scared the mechanic that let me use his lift, told him the groan&moan was worse, with clunks...
The quick look on his face was priceless !!!! (only fooled him for a second)

The AC Delco stuff with the modifier already in it never gave my SS any issue for 18k miles.

For the M6, use Redline D4.

Yeah, but 3 places around here price was almost $30 for a qt of 10-4034.
(close to $60) No one had it in stock, dealer included.
With the CRC modifier, and 2 qts of super-tech 75w-90, was about $21 total.

Don't care, no quart of gear oil is worth $30, and the stuff they put in the trucks; 10-4016, WITHOUT the modifier sells for $30 as well. (???wtf???)
Second time yesterday, growl is gone, period.

You can find it for about half that online. Is the super tech even synthetic?

Did something change from 17 to 18?

Amazon is telling me the AC Delco Dexron LS 75W-90 is compatible for 17s but not 18s. :twitch: