So, I've spent the last hour looking at countless threads on various forums regarding differential fluids in the various GM applications. We have owned three 1999 Tahoes, all of which we have used Valvoline 75w-90 in both the front and rear differentials. We live in a climate where we can easily see below zero temperatures at night during winter (upstate NY). As I understand there is a lot of debate on what to use in the rear differential (G80). My front diff hadn't been changed in several years so I had it done today with Valvoline 75w-90 fluid like usual. Even their non-synthetic gear oils now say "limited slip" on the bottles. Not sure if that means it has an additive in it. Is this OK for the front diff? I really would love to put to bed what exactly to use in the rear. I have a new OEM cover (old one is leaking) and LubeLocker seal ready to go on it. Thanks!
Differential Fluids...
- Thread starter derekjl
- Start date
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Yukon John
Full Access Member
I used Valvoline for years...good stuff. I switched to Lucas a few years back when I had a whine develop in a G80...never looked back.
http://lucasoil.com/products/gear-oil/synthetic-gear-oil/lucas-sae-75w-90-synthetic-gear-oil
Honestly though....I have no COLD weather experience with any of the gear oils...I have been in Tropical South Florida for 40 years...that being said, if Valvoline works for you in your climate...stick with it.
http://lucasoil.com/products/gear-oil/synthetic-gear-oil/lucas-sae-75w-90-synthetic-gear-oil
Honestly though....I have no COLD weather experience with any of the gear oils...I have been in Tropical South Florida for 40 years...that being said, if Valvoline works for you in your climate...stick with it.
Thanks for your reply. I guess my main question was it is ok to use this specific fluid in the front differential since it seems to contain an "additive" that GM doesn't recommend using. I'm not sure if they only don't recommend it for the G80 rear or if that includes the front also. This entire topic seems to be highly debated for many years online.
mizzouguy
Full Access Member
I've used mobil-1 75-90 and royal purple 75-90, both which come with a limited slip additive, in both the front and rear and never had an issue. It's seen below 0 and above 100, and towing.
Not to steer my own thread off topic, but I'm also going to get the transmission fluid done. From what I understand Dex III has been replaced by Dex VI. Is this the only acceptable fluid for the 4L60E or are there others? I know Valvoline makes a Dex/Merc ATF and also a "high mileage" version with stop leak. My tranny has 35k miles on it and the fluid has never been changed since it was installed.
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Just order the DEXRON IV on Amazon, I get the AC Delco DEX6 for $22 a gallon with free shipping. I use it in all 3 of my trucks.
Here is the link: https://www.amazon.com/gp/product/B01EKMGG92/ref=oh_aui_detailpage_o06_s00?ie=UTF8&psc=1
Here is the link: https://www.amazon.com/gp/product/B01EKMGG92/ref=oh_aui_detailpage_o06_s00?ie=UTF8&psc=1
mizzouguy
Full Access Member
Assuming the tranny shop that did the install used dex-vi, his suggestion ^^^ looks like a good option. If the shop used dex/merc, I'd put that back in it unless you are doing a full flush. They will mix but I prefer one or the other not a combo lol.
