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Discussion Starter · #1 ·
350990
Howdy folks,

I am trying to change the fluid in my differential. 'G80' is present in the glove compartment codes, meaning that I have a G80 differential. Attached here is my rear differential. Btw, this is on a 1999 Chevy S10 LS 4wd with the 4.3 V6

And also, would 75w-90 gear oil with no LS additives be okay to use?
 

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I believe LSD additive is for diffs that utilize a clutch pack to provide the locking.
The G80 is a mechanically locking differential that uses flyweights instead of friction for locking.

According to what I found on the silverado/sierra forum. They suggest 75w-90 gear oil without LS additive.
I personally used Amsoil Severe Gear on my open diff.

Sources:

Post #4
 

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This age old question comes up every so often..is it an lsd or not....does it have friction discs....or not. Here's an animation that answers those questions.

EDIT: note the friction discs.

 

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Would a 7.625 cover and gasket work?
I wouldn't mess with a gasket. I used Perma-Tex The Right Stuff in an aerosol can a few weeks ago...Ready for use in in about 7 m minutes.
 

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Discussion Starter · #8 ·
I believe LSD additive is for diffs that utilize a clutch pack to provide the locking.
The G80 is a mechanically locking differential that uses flyweights instead of friction for locking.

According to what I found on the silverado/sierra forum. They suggest 75w-90 gear oil without LS additive.
I personally used Amsoil Severe Gear on my open diff.

Sources:

Post #4
So would this work?

350999
 

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From what I've been reading here and on other forums. If my truck had a G80 I would feel comfortable using that gear oil.
 

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Gm has had a couple TSB's regarding the G80. The oldest one said don't use any LSD additive as it could ruin your differential. Then 10 years later they issued one stating that if your G80 chattered to add the additive. The current thinking is you don't need the additive so don't add it.
$14 a quart is a bit much for conventional gear oil. What makes STP brand worth the extra. I use Valvoline $5 a quart conventional gear oil in all my G80's.
 
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This is what a person I know at a dealership told me for my 2003 S10 with a G80.

GM 88900401 do not use LSD additives.
 

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Just looked up (GM 88900401). I'm going to start using that. Even tho' it's $25 a quart the Grape Scent makes it a whole lot better than that horrible gear lube stench.
 

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Discussion Starter · #13 ·
Gm has had a couple TSB's regarding the G80. The oldest one said don't use any LSD additive as it could ruin your differential. Then 10 years later they issued one stating that if your G80 chattered to add the additive. The current thinking is you don't need the additive so don't add it.
$14 a quart is a bit much for conventional gear oil. What makes STP brand worth the extra. I use Valvoline $5 a quart conventional gear oil in all my G80's.
It was on sale for $7, that's why I got it :LOL:
 

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Just looked up (GM 88900401). I'm going to start using that. Even tho' it's $25 a quart the Grape Scent makes it a whole lot better than that horrible gear lube stench.
Check the dealership they can usually get it cheaper. At least my local dealership can.

Mine was already serviced by someone before because it has a brand new diff cover but I don't trust what is in it because I don't know if they put the additive or not so I will be using the fluid number given to me.

I figure why risk it there is so much debate on the topic of G80 diff fluid just go with what the dealership uses and be done with it. GM obviously gives the dealerships technical data so I would trust that over random posts on the internet that constantly conflict posts before or after it.

Pay the few extra dollars for the peace of mind. And of course I recommend everyone to call their dealership and verify the number given to me is the same number they recommend because it doesn't hurt to get extra verification.
 

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Is there anything wrong with your current cover? Unless it's rusted or damaged, the original one is probably better quality than a cheap aftermarket one. I would just clean it up and reuse it.
 

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Is there anything wrong with your current cover? Unless it's rusted or damaged, the original one is probably better quality than a cheap aftermarket one. I would just clean it up and reuse it.
His is a bit rusty from the pictures. I would replace it myself if it were mine. They also love to rust behind the gasket material.
 

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This thread has a bunch of rear end info...along with a pic of all 3 covers.

 
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