: My 2004 CTS-V has 47.000 miles and I do not know if the rear diff fluid



Tackelbarry
05-20-12, 12:02 PM
has ever been changed. I am not having any problems, but would feel better knowing that all of my fluids are fresh. I picked up some Valvoline 75/140 full synthetic for a limited slip differential. It says it is GL-5. Is this as good as the O.E. and does it have the friction modifier already added? I am planning to swap the fluid this afternoon. Thanks for the input.

FuzzyLogic
05-20-12, 01:12 PM
Any GL-5 is better than the black sludge that you have in there now. 75W-140 is better for the life of the differential and will quiet it down some.

I can't say this enough--do NOT remove the differential fluid drain bolt until you break the fill bolt free. I did my first differential fluid swap after 7k miles and had to brace my feet against the jacks and almost crapped my pants straining to break the fill bolt free for the first time.

As far as the, "is it the best fluid available" question, I'd say no. Having changed that fluid three times with three different brands (my CTS-V has 23k miles), I'd recommend Redline 75W-140 next time. Exceeds GL-5 specifications.

http://www.redlineoil.com/product.aspx?pid=134&pcid=4

Tackelbarry
05-20-12, 04:49 PM
Thanks for the advice Fuzzy. I broke my upper/fill bolt loose first and then the lower drain bolt. I went ahead and used the 75/140 Valvoline synthetic, since I already bought it. I am going to start looking for the best place to buy the Redline so I can have it on hand for the next time.
My fluid was a light brown color but not as bad as I had expected. When I test drove the car it almost felt like there was less rollong resistance or a hair more power. Is that possible or was I dreaming? Either way, I feel better knowing that another one of my fluiids is fresh. Next will be the transmission fluid. Any suggestions? Thanks again.

FuzzyLogic
05-20-12, 06:05 PM
You're absolutely not dreaming. That initial fill that GM put in the car seems to degrade really fast--especially since break-in on the differential during the first couple of hundred miles spews tiny shards of metal into the oil right away. When I first changed my differential fluid, I went with Royal Purple MaxGear (75W-90) and it felt like I lost 200 lbs in the rear end of the car when turning.

Since then, I've learned that Royal Purple is really, really bad oil with really, really good marketing and avoid them like the plague. I bought a gallon of Redline 75W140 (Part #57915 - two changes worth) at JDM Hub, which looks trashy but turned out to be okay. $57.

As far as transmission fluid goes, I've been through at least 4-5 different types of fluid, and finally wound up talking to Shane at Thunder Racing (owner and CTS-V driver). He recommended 3 quarts of Redline D4 ATF (http://www.redlineoil.com/product.aspx?pid=51&pcid=7) and 1 quart of Redline MTL 70W80 GL-4 (http://www.redlineoil.com/product.aspx?pid=45&pcid=7) gear oil for lower mileage T56 transmissions, transitioning to half and half D4 ATF and MTL on higher mileage transmissions--especially if you start to experience a lot of "diesel"-type noise.

Compared to the stock transmission fill, I found that Royal Purple's Synchromax felt and sounded about the same, Mobil 1 ATF was very loud, and the combination of Redline ATF and MTL was very quiet. I haven't seen the ATF/MTL mixture coming out of the transmission yet, so I can't provide impressions on the back end, but so far, it's the best solution I've found.

Tackelbarry
05-20-12, 07:10 PM
Thanks again, Fuzzy. You are definately an asset to this community!

FoD
05-20-12, 07:34 PM
Wrote everything down...doing all of this stuff over the weekend.

FuzzyLogic
05-20-12, 11:07 PM
Thanks again, Fuzzy. You are definately an asset to this community!

No problem! Just trying to contribute back to the place that helped me out so much when I needed help.

odthetruth
05-21-12, 01:47 AM
has ever been changed. I am not having any problems, but would feel better knowing that all of my fluids are fresh. I picked up some Valvoline 75/140 full synthetic for a limited slip differential. It says it is GL-5. Is this as good as the O.E. and does it have the friction modifier already added? I am planning to swap the fluid this afternoon. Thanks for the input.

I have Valvoline 75-140 in my diff now. I changed it a few hundred miles back. Make sure to add friction modifier, even though it states it comes with it for the diff. I didn't, and I have a very tiny whine. Its been running perfect otherwise though, and feels good in all driving conditions so far.

You'll need a 10mm allen key, drain pan, and a suction gun.