rear differencial fluid

bballa · June 10, 2004

Is there a definitive answer as to wether or not mobil one gear oil can be used in a G80 rear end without having to add an additive. Mobil one web site states that it will work in locking differencials but says nothing about meeting GM specification 9986115 (from my owners manual).

asepgrad98 · June 10, 2004

i just changed mine last month. Bit the bullet and bought the GM synthetic (over 20$/qt holds 2.4 qts). Its only money right.

bballa · June 10, 2004

The parts dept. at the local dealer wants $27 qt for the GM stuff. I asked why when after market lube costs about $8 qt. He said that is what GM charges them and that he didn't know of any difference between the GM gear oil and any after market synthetic gear oil. He also said that no additive was necessary since the G80 uses gears and not plates. I do not believe I can trust him on that. I'm still thinking on going with mobil one. Easy to get at a decent price.

juicy · June 11, 2004

i have a LSD and i added 2 bottles of friction modifier..

i dont care it it says it has it or not, im not taking any chances..

and get the 80W-140

none of this 40-90 crap

use the HD stuff

snoman · June 11, 2004

i have a LSD and i added 2 bottles of friction modifier..

i dont care it it says it has it or not, im not taking any chances..

and get the 80W-140

none of this 40-90 crap

use the HD stuff

Unless you are operating in extreme temps or conditions that casues very high oil temps, they is nothing gained with using 85w140 over 80w90 "crap" . Actually, you may loose a little MPG with the thicker stuff too.

chris_kucia · June 11, 2004

He also said that no additive was necessary since the G80 uses gears and not plates. I do not believe I can trust him on that.

Unless I misunderstand my service manual, the G80 has two clutch packs consisting of layered alternating clutch disks and plates.

snoman · June 11, 2004

Unless I misunderstand my service manual, the G80 has two clutch packs consisting of layered alternating clutch disks and plates.

You are correct. He needs a new mechanic!

bballa · June 11, 2004

The guy I spoke with works in the parts dept. I dont think he is a mechanic but I thought he might have some knowledge on the subject. My mistake!

Valsport · June 11, 2004

in a G80 locking diff NO ADDATIVE IS NECESSARY. I've been using Mobil 1 75W-90 and Royal Purple 75W-90 in three different G80's (1997 Tahoe, 2001 silverado, 2003 Silverado). These lubes are far superior to GM's synthetic gear lube, plus they're less than half the price. I've talked with both Royal Purple's and Mobil's tech support to confirm this, as well as the head mechanic at my chevrolet dealership.

snoman · June 11, 2004

Additive is not a must have but it can help plate "grippyness". It is not a bad idea in diffs than use friction based clutch plates to control slippage.

bigdogs · June 11, 2004

You can also go with Amsoil Series 2000 which has the friction modifiers already mixed in and still a WHOLE LOT CHEAPER than the GM stuff.

Mort · June 12, 2004

You can also go with Amsoil Series 2000 which has the friction modifiers already mixed in and still a WHOLE LOT CHEAPER than the GM stuff.

When I went on Amsoil to check the Specs for my truck I found that they do not Spec an oil for the G80 option in our trucks.

Amsoil says:

Differential, Rear Others....GLS[4]

75W-90

Gear Lubricant,Special - Not Available Through Amsoil

Notes:

4. GLS is synthetic lubricant; use only GM part

So I guess if you use Amsoil series 2000 or their other Series or Mobil 1 as well you are on your own as they do not specifically recommend a product for this application.

I bought the GM fluid and my dealer gave me 44% of list. I can get it cheaper than Amsoil from the dealer.

bigdogs · June 12, 2004

Amsoil is rated GL4 and GL5 for both their normal synthetic gear oil as well as their series 2000. As for Mobil 1 I looked at a bottle today and says it works with limited slip so that implies it does not need anything additional either. The price is about the same for me, Amsoil is $7.20/qt (series 2000) and Mobil 1 is $6.85/qt.

titanium10k · June 15, 2004

About one year ago i ordered some of the gm stuff from gmpartsdirect.com. it was half the price of the dealer but i checked the other day on their site and they now cant ship it because the containers arent sealed..does anyone know a good place to purchase this stuff at a good price....also anyone know where a good place is to purchase an air filter for these trucks ????