Limited slip additive or not?

[Rocket Man]

So,...did we ever decide whether or not to use an additive on a G80? My shop just added it to my G80 rear along with DELVAC 1 75/90. Did they mess up?

It doesn’t need it but I don’t think it hurts anything either.

 

[Jolly Roger]

It doesn’t need it but I don’t think it hurts anything either.

Spent about 5 hours last night reading and scouring all corners of the net on this issue, even letters from Eaton from people who have written them about it. Any additive in the G80 is considered a contaminate and should be flushed and refilled with strait up Synthetic 75-90.

Here are just a few of a hundreds of forums I stumbled on...
https://www.chevytalk.org/fusionbb/showtopic.php?tid/256237
https://www.gmfullsize.com/threads/g80-posi-rear-end.113129/
https://www.chevytalk.org/fusionbb/showtopic.php?fid/34/tid/309587/
https://www.gmtruckclub.com/threads/g80s-do-not-take-friction-modifier.802564/

 

[Rocket Man]

Spent about 5 hours last night reading and scouring all corners of the net on this issue, even letters from Eaton from people who have written them about it. Any additive in the G80 is considered a contaminate and should be flushed and refilled with strait up Synthetic 75-90.

Here are just a few of a hundreds of forums I stumbled on...
https://www.chevytalk.org/fusionbb/showtopic.php?tid/256237
https://www.gmfullsize.com/threads/g80-posi-rear-end.113129/
https://www.chevytalk.org/fusionbb/showtopic.php?fid/34/tid/309587/
https://www.gmtruckclub.com/threads/g80s-do-not-take-friction-modifier.802564/

Yep I shouldn’t have said anything because it’s a hornets nest. There’s just as many threads where guys swear it’s not only harmless in the G80 but needed, and plenty of guys have added it without any negative consequences since it’s so confusing. My suggestion is do what you feel is right after reading for 5 hours. I will forever keep my mouth shut on the subject, there’s plenty that’s been written in it. It’s just confusing as hell. If you had that done at a shop, I would ask them to flush it and put the fluid in that has the correct specifications without the additive.

 

[Jolly Roger]

Yep I shouldn’t have said anything because it’s a hornets nest. There’s just as many threads where guys swear it’s not only harmless in the G80 but needed, and plenty of guys have added it without any negative consequences since it’s so confusing. My suggestion is do what you feel is right after reading for 5 hours. I will forever keep my mouth shut on the subject, there’s plenty that’s been written in it. It’s just confusing as hell. If you had that done at a shop, I would ask them to flush it and put the fluid in that has the correct specifications without the additive.

Yes the confusion about the subject is why I kept reading until I felt I got to the bottom of it all.....Total hornets nest is right! LOL.
But I truly appreciate you answering Rocket Man.

 

[Jolly Roger]

.....There’s just as many threads where guys swear it’s not only harmless in the G80 but needed.....

I have found the opposite.

I have no dog in this race...

I just want the right damn lube in my punkin! LOL


https://www.tahoeyukonforum.com/threads/whining-noise-through-acceleration-help-video.120467/

 

[Rocket Man]

I have found the opposite.

I have no dog in this race...

I just want the right damn lube in my punkin! LOL


https://www.tahoeyukonforum.com/threads/whining-noise-through-acceleration-help-video.120467/

Here’s some fuel for the fire. There’s a whole lot of threads out there that swear the fluid with GM’s spec GL-5 already has the LS additive in it. This is from Bob Is The Oil Guy’s website. I’m not saying it’s accurate but this is part of the reason there’s so much confusion, and I never could get to the bottom of it. All I know is I use AC Delco synthetic fluid spec’d for the G80 so I don’t have to look up any more confusing info. Does it have the LS additive in it? I do not know. I just know it doesn’t need anything added lol. Quote:
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.

This shit is the reason I quit trying to figure it out.

 

[Jolly Roger]

The fact that the G80 RPO code is also used to indicate posi or limited slip differentials in car applications, but in trucks it is the Eaton Gov-Loc certainly adds to the confusion about all this but after 5 hours of Non-biased reading last night I feel I have sifted through the BS and consolidated all the "most intelligent" answers into one pile. The consensus is..... NO friction modifiers in a G80 Gov-Loc.

However my shop and two of the gear shops in my town both say they use a additive in all Gov-Locks.

 

[Rocket Man]

The fact that the G80 RPO code is also used to indicate posi or limited slip differentials in car applications, but in trucks it is the Eaton Gov-Loc certainly adds to the confusion about all this but after 5 hours of Non-biased reading last night I feel I have sifted through the BS and consolidated all the "most intelligent" answers into one pile. The consensus is..... NO friction modifiers in a G80 Gov-Loc.

However my shop and two of the gear shops in my town both say they use a additive in all Gov-Locks.

Well there ya go lmao.

 

[Jolly Roger]

Well there ya go lmao.

Yeah, well its still not comforting when GM says.....

"The use of any additive in locking rear axles (G80) is not recommended. Rear axle additives are designed for use in limited slip differentials which are normally installed in cars. All light duty trucks equipped with RPO G80 make use of a locking differential and the use of additives will delay the engagement of the locking mechanism and may decrease axle life."

 

[Jolly Roger]

Another confusing link..
https://www.gm-trucks.com/forums/topic/183167-g80-gear-lube-eaton-phone-call-today/