Limited Slip Additive needed for G80?

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Nick1994

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This is for the 2002 Chevy Trailblazer LTZ. Has the G80 with LSD and 3.73 gears (2wd).

Does it need the additive or is Mobil 1 or Valvoline gear oils enough if they say "for LS"?

75w90 a good viscosity for it?

Going to get a Fel-Pro gasket, I don't need RTV right?

Thanks.
 
The g80 is an automatic locking differential, not really a limited slip. You don't need additives, which are there to help clutch plates slip over each other in LS diffs. You don't want the g80 clutch pack to slip.
 
It's a Eaton Gov-Loc "Governed Locker" No additive needed, I use Mobil 1 75w90 LS in my 11.5" Gov-Loc with no issues. Though some people have say they have noise issues for some weird reason.

Check for a drain plug, The Corporate 8.5" differential in early GMT800 Trucks had drain plugs, Not sure about the 8.5" in GMT360's
 
G80 is an option code that GM has used for many years - Positraction, Safety Trac, other names were used. At least 40 years, probably even longer. Depending on the age and version of your vehicle, some definitely require the use on a GM or similar additive, others do not. Best to check with dealer, manuals, or other good source to be sure. No one size fits all here.
 
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This is what dnewton advised me about the G80 in my '02 Suburban (http://www.bobistheoilguy.com/forums/ubb...han#Post3140059)

Originally Posted By: dnewton
Rear diff:
GM's fluid spec (9986115) is merely a designation of a syn 75w-90 with LS additive, and nothing more. There is a quote from a guy named Michael Torrenson (or something similar to that) who worked for Eaton, where he indicates that ANY GL-5 fluid will be OK for a GM G-80 diff, and the only concern is to make sure you use one with a LS additive, because the G-80 "locker" actually has a clutch engagement system. Just about any decent GL-5 lube will work here, but syn's are going to give you a longer OCI, so they might be worth the investment. Most of the syns, and some of the dinos, will have LS additive already included. Of note, the 80w-90 Valvoline does I know for sure, because I just put some in my Ford diff this weekend. If you live in super-hot areas, AND you town for the MAJORITY of the operational time, then I'd "upgrade" to a 85w-140. But ONLY if you meet BOTH of those criteria. If you don't, then use a 75w-90 syn or 80w-90 dino that meets SAE J2360. Adjust your OCI to your fluid type. If you have a G-80 locking diff (and most did) then you must use a LS compliant fluid. You will need to either buy a fluid with LS additive included, or put it in separately. Regardless of what others state, the G-80 does have clutches. They often mistakenly think that the "locker" is a mechanical type, but it is actually a pawl-operated clutch system. It has clutches. You need LS additive if you have a G-80.

So I'd go with an LS fluid or add an LS additive. Of the two choices you listed, I'd go with the Valvoline, which is on the J2360 list dnewton referenced, whereas Mobil 1 is not (but Delvac is!).
 
In 3 decades of 4WD - G80 is a classic - I drive all over town and it never makes a sound - and on 10 miles of dirt road I give it a nudge on turns and straight ahead - always two "stripes" - and in the sand/soft stuff ? go really far before I press 4x4 ...
(No LS - Delvac for me)
Once again - companies in the big leagues helps us out on the "farm teams" ...
 
Changed it on Sunday. Ended up using Valvoline Synpower 75w90 LS. Road trip on Friday, 900 miles round trip so we'll see how it does.
 
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