rear/front differential fluid

[yeehoo]

I planning on changing diff fluid and finding conflicting info as to if I need ls additive or not. 1993 K1500 rpo code in glove box is GT4. I do not see G80 anywhere on sticker.

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[df2x4]

Do not use any friction modifiers or additives in the gear oil of any GMT400 differential. Especially a G80. There's a GM service bulletin that's been floating around the internet for a long time about this issue.

The correct fluid for both front and rear is GL-5 rated 80W-90, like this.

https://www.amazon.com/gp/product/B007Q10F3S

 

[yeehoo]

thanks df, went with 80w90. Unfortunately, the people that owned it before me stripped the rear diff fill plug. I guess i will have to get a cover that has a fill and drain plug.