Differentials.. 75w-90 vs 75w-110

[Supercharged111]

I was not aware of this TSB. That tosses any theories out the window.

 

[Schurkey]

I want to switch to AMSOIL Severe Gear in both the front and rear diffs.

How? Most gear oils have posi additives so I don't see what would make Amsoil so exclusively incompatible here.

Mistake in logic. I didn't say that Amsoil was somehow special in it's incompatibility. I referenced Amsoil since the OP specifically mentioned it, and because I have experience with it.

ANY gear lube--synthetic or mineral--with "posi additive" will be unsuitable for a G80 rear axle. At this point, I don't think the thread-starter has ever confirmed that he has or does not have a G80.

And since there is no posi present, what is there to hurt? The while point of a posi additive is to have the right amount of friction present to allow it to do its job. No additive means the posi won't slip enough. What does additive present mean for a non-posi? Jack **** from where I'm typing, but I'm willing to learn if I'm wrong.

IF (big IF) there's a G80 involved, it's got clutches that will be contaminated by the "posi additive" and they won't work (grip) properly.

Guys cry endlessly about how the G80 is a "Locker" and not a "Posi" or a "Limited Slip". Which is fine, except that each of them use some sort of clutch assembly--either multi disc or cone. There's differences in how the clutches are engaged, and there's apparently some difference in the clutch friction material. The friction material or the engagement mechanism in the G80 clutches isn't compatible with "posi additive".

I have not seen any technical specs on various gear oils, but when I've read the backs of containers, it looked more like carefully worded marketing, that says it could be used with positrac differentials not that it actually included a modifier.

But it's the modifier ("posi additive") that makes it compatible.

The last bottles of gear lube that I bought--specifically because it did NOT seem to have
"posi additive" said that it was compatible with posi differentials but only if the fluid was being "topped off", not a full drain-and-refill.

I believe the G80 uses some sort of clutch mechanism to engage the lock.

The governor engages the clutch packs, the clutch packs lock the differential. But the important thing is that there's clutches, and those clutches are allergic to "posi additive."

 

[Schurkey]

"at the ends of the axles tubes".... I'm confused on the location. The only gasket I'm aware of, is not really on the tubes, but between the axle shafts and the hubs, in the case of a full floating axle.

Good catch. I was looking at the service specs for a 10.5 (full-float) axle when I stumbled on that tidbit about synthetic oil being incompatible prior to a certain build date.

I'm not familiar with semi-floating axles. I can't picture where a gasket would go, assuming you're talking about a flat paper type gasket.

You're right. The ends of the semi-float axle would not have a paper gasket or silicone sealer that would be exposed to gear lube.

'Course plenty of folks use RTV silicone on the differential cover. I've never heard of synthetic gear lube damaging the silicone sealer on the cover--so I don't really understand why they're so wild about silicone on the hub/axle. But they are, and I'm just passing that along.

 

[evilunclegrimace]

The governor engages the clutch packs, the clutch packs lock the differential. But the important thing is that there's clutches, and those clutches are allergic to "posi additive."[/QUOTE]
Thank you! Finally sone one understands

Mistake in logic. I didn't say that Amsoil was somehow special in it's incompatibility. I referenced Amsoil since the OP specifically mentioned it, and because I have experience with it.

ANY gear lube--synthetic or mineral--with "posi additive" will be unsuitable for a G80 rear axle. At this point, I don't think the thread-starter has ever confirmed that he has or does not have a G80.


IF (big IF) there's a G80 involved, it's got clutches that will be contaminated by the "posi additive" and they won't work (grip) properly.

Guys cry endlessly about how the G80 is a "Locker" and not a "Posi" or a "Limited Slip". Which is fine, except that each of them use some sort of clutch assembly--either multi disc or cone. There's differences in how the clutches are engaged, and there's apparently some difference in the clutch friction material. The friction material in the G80 clutches isn't compatible with "posi additive".


But it's the modifier ("posi additive") that makes it compatible.

The last bottles of gear lube that I bought--specifically because it did NOT seem to have
"posi additive" said that it was compatible with posi differentials but only if the fluid was being "topped off", not a full drain-and-refill.


The governor engages the clutch packs, the clutch packs lock the differential. But the important thing is that there's clutches, and those clutches are allergic to "posi additive."

Thank you! finally someone understands the operation of a G 80 locker.

 

[454cid]

Good catch. I was looking at the service specs for a 10.5 (full-float) axle when I stumbled on that tidbit about synthetic oil being incompatible prior to a certain build date.

Do you happened to remember what that build date is? I always figured mine was filled with synthetic, but I've put regular in it.

'Course plenty of folks use RTV silicone on the differential cover. I've never heard of synthetic gear lube damaging the silicone sealer on the cover--so I don't really understand why they're so wild about silicone on the hub/axle. But they are, and I'm just passing that along.

Maybe it's longevity through the warranty period that GM is worried about.

 

[454cid]

Thank you! finally someone understands the operation of a G 80 locker.

I understand perfectly. I'm not sure why you have a problem. Maybe my wording isn't precisely to your liking?

 

[evilunclegrimace]

I understand perfectly. I'm not sure why you have a problem. Maybe my wording isn't precisely to your liking?

I do not have a problem and it is more than obvious that it is you whom does not understand.
It is not your wording, it is the fact that you refuse to admit that the governor is what engages the clutch packs. You do not seem to understand the operation of a G80 locker and want to be augmentative for the sake of argument. You are free to wallow in your ignorance, I will have nothing else to say to you. Have a nice day.

 

[Supercharged111]

So what happens when the clutch packs get old and worn out? Can you get replacement parts for the diff?

 

[evilunclegrimace]

So what happens when the clutch packs get old and worn out? Can you get replacement parts for the diff?

Yes you can get parts but it is very expensive to rebuild the G-80, you are better off installing a different style unit

 

[Schurkey]

Do you happened to remember what that build date is? I always figured mine was filled with synthetic, but I've put regular in it.

I looked back at some likely sources, but...no...I don't have a specific date.

Maybe it's longevity through the warranty period that GM is worried about.

Maybe. Like I said...it just doesn't make sense to me.

So what happens when the clutch packs get old and worn out? Can you get replacement parts for the diff?

I suspect that GM sells--or sold--replacement parts. I don't know if they're discontinued by now, or still available.

Same deal with aftermarket parts. I suspect they're available, but I haven't looked to confirm.