question on differential fluid

Hi everybody, I'm planning on changing the fluids in both differential this weekend. (90 k1500 700r4, 5.7l). I am a bit confused as to what to put back in. The gear
oil that I bought at autozone is 80-90 gl5. I am bothered by the small print on the bottle that says "for limited slip top off only". What kind of fluid should actually be in this truck? Am I correct in assuming it's the same in both differentials? tia, Chris
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what that's saying is if you have a limited slip, only use the fluid to top off an already full diff case. if you don't have a LSD, don't worry about it.
-Bret

gear
print
fluid
in
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I checked the rpo codes in the glove box. and found GQ1-standard Ratio axle, G80-limited slip rear diff, GU6-rear ratio 3.42. I then called the local dealer and he ran the VIN and got the same info. He advised me it should be a 3.4 limited slip and that I would need an additive for the GL5 lube. Thanks for the help, Chris

(90
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"Chris" wrote

axle,
He
additive
Just for your info.....GM doesn't recommend using the "limited slip" additive on the G80 truck diffs. It's old news now, there was a bulletin out on this issue a few years ago.
Ian
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Thanks for the info, I wonder why the local guy here did not know that.
Chris

this
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"Chris" wrote

I don't know. But I've run into a lot of dealership tech's that aren't aware of this bulletin. I don't think it will do any real harm to use the additive, as we used it for years before the bulletin came out. But now the official policy is that it's not necessary for the Eaton locking rear diff. It still is used for the older "limited" slip rear axles.
Ian
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Thanks again for the info. I'm glad there are guys like yourself on this newsgroup. There's always something to learn.
Chris

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