Additive for limited-slip differential

Ok want to change my fluids in my differential's (99 k1500 suburban) the owner's manual says that if it a locking differential that it does not need the additive , but the dealership's and auto stores says it does need it.
Whould it hurt to add it are should i leave it out. Im kinda confused on who is right owners manual are every one else that i spoke to? im kinda leaning to every one else.
tia
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If its a locker (G80 code) no additive. Lockers don't need additive limited slip do. They are not the same thing. So if you said "do I need additive for my limited slip" then the people that answered yes were correct. But you don't have a limited slip(posi) unit.

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I have a 99 Z71 and it has the G80 rear end. My book says it has to have synthetic but says nothing about an additive. Now, you've tossed another term in the mix. What is a "locker?" I thought the G80 means that it is limited slip. .

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Humm where is this (G80 code) how do I find out what my differential is? My owner manual doesn't say any thing about a limited slip it just mentioned the locking and regular kind,but the when I checked with some dealerships and I have gave them the vin code and they tell its limited-slip so i dont know if i should are shouldnt add the additive right now. Is there some numbers on the differential themselfs that i could look up and know for shure what it is??

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The code is a "RPO" code. Its on a sticker inside the glove compartment. There are a bunch of codes on that sticker. Now I gotta go get my book out of the truck to find out what a Locker is. .

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first, look in your glove box for the service parts identification sticker, look for G80, if it's not there, GM put an open diff in it, and someone else changed it later on. in that case the only way to tell is to pull the diff cover.
traction.eaton.com click on mechanical locking differential. Eaton makes the G80.
-Bret
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A locker locks both wheels together no matter what. The G80 is a part time locker. If one wheel speed is 50rpm faster than the other it will lock them together. (Only operates at speeds below 20mph). This makes it streetable. A limited slip (aka posi) has both wheels tied together with a clutch system that allows slippage for cornering etc. This needs an additive so it slips the proper amount.A limited slip will slip with one wheel on ice and one on pavement. A locker will not. Pull up to a sturdy wall, jack one tire off the ground, put it in drive and if you can smoke the tire on the ground you have a locker.I don't think a limited slip is an option with Chevy trucks.

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Gary and the gang have talked about this one many times. Here is a link for some past dirt that was unveiled.
Derek
May have to cut and paste the link if it doesn't work right.
http://groups.google.com/groups?hl=en&lr=&ie=UTF-8&oe=UTF-8&threadm=xX5p9.104051%24DN4.15402%40sccrnsc01&rnum=1&prev=/groups%3Fq%26lr%3D%26ie%3DUTF-8%26oe%3DUTF-8%26selm%3DxX5p9.104051%2524DN4.15402%2540sccrnsc01%26rnum%3D1
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"kdm" wrote

The owner's manual is right. The dealership boys should know better, but I suppose they haven't been reading their paperwork for the last few years. You have the Eaton locking rear end, and it does not require the additive. I doubt anything bad will happen if you put it in....as we used to install it all the time, until GM mentioned that it was not necessary.
Ian
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I would like to thank every one for there help. I took a look at the code today and it is the G80 so I want be adding anything but the oil in it. Now I just have to find recipe for the additive they already sold me.

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I ran into the same problem with my dealer and my 96 K1500 with limited slip rear axle. The GMC dealer put additive in when my owner's manual said no. After we all consulted the official GM workshop manual - which says clearly NO additive - the dealer drained the differential and filled it with the prescribed oil only. That was 65000 miles ago.
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