BLACKND

iTrader: (5)

Gotta a question here. I am changing out my fluid this weekend on the rear end. Got the G80 in it. I went and picked up the fluid yesterday and trusted that the damn parts department knew what they were doing. Well, they didn't. They gave me 80W90 axle lubricant---Non-Synthetic, and the limited slip additive, and they gave me 4 quarts of the damn axle lubricant. WTF? Anyways, thinking that this wasn't right, I called another dealership this morning to check them out and they confirmed that it calls for 75W90 Synthetic Axle Lubricant, but said the limited slip additive was not needed. WTF? So whats going on, I know the 75W90 is what I need, but does it seriously not need the LS Add? I am trying to cure this Limited Slip Chatter that I am getting. Also, this stuff from GM is like 25 bucks a quart. The mobile one is like 9 bucks a quart. Anyone use the mobile one 75w90 and could I run the mobile one synthetic with gm limited slip additive?

Mort

You do not need any friction modifier with the G80 Locking Differential. My manual says to use SAE 75W-90 Synthetic GM Part# 12378261 or equivalent meeting GM Specification 9986115.

Does Mobil One 75W90 meet GM Specification 9986115. If it does then you can use it. I have read of other people using Mobil One and have not heard of any problems but the responsibility would be up to you.

Not sure why you are getting chatter in the G80 as it does not have the same clutches as a Limited Slip. I think it only has enough of a clutch to engage the ramping system to lock it up.

BLACKND

iTrader: (5)

Well, its only happened once, so I'm not real sure either. But the whine from my gears is starting to get louder. I guess the chatter that one time could have been the locker engaging and disengaging while I was coming to a stop.

Mort

Most of the time it will work seemlessly and you will not be aware of it engaging or disengaging. Under certain circumstances you may be able to feel it engage. When mine was new I could feel and hear it drag a bit around corners but not since it has worn in some. Sometimes it feels like a wheel is dragging a bit but it is not supposed to engage until there is a 100 rpm difference between the rear wheels so I am not sure if a wheel is dragging or not. Over 20 mph it is supposed to work like an open differential.

When I chaged the fluid in mine it had quite a lot of shavings and metal filings in it. So after I drove it a while I changed it again and did not find and shavings or metal filings. So the shavings and filings were either from braking it in or left in it from machining. It looked like some of each to me.

SnakeOiler

iTrader: (6)

I just did my maintenance last night (80,000 mile). I've always used Mobil 1 75W/90 without the additive.

Mr. Sandog

The G80 uses synthetic without additive. The full Eaton LSD must run on 80/90 with additive.

moregrip

iTrader: (8)

I doubt 80w90 will be an issue for you. What I was told about the g80 was to run it without the additive first, if it starts to chatter, add some. Sometimes you need it, sometimes you don't. Many people run the g80 with no additive.

budhayes3

iTrader: (19)

No additive for the G80, but from what I've been lead to believe, synthetic is imperative. Mobil1 syn 75w-90 should be fine.

BLACKND

iTrader: (5)

Yeah I got the mobile 1 synthetic. Get this took that other stuff back to the dealership and they were going to replace that with the 75w90 like needed. So the guy brings out 3 quarts of mobile one synthetic. He told me I was going to owe him 80 something bucks. WTF???? They were trying to charge me 28 bucks a quart for the same exact **** that I could buy at autozone for 8.50. I told him to refund me and drove right across the street to the zone.

moregrip

iTrader: (8)

let us know how it works out when your done switching it over