What is the oem grease used in a 8.5" GN rearend?

[troyk]

I assume it is non-synthetic? What weight?
I already have the GM additive.
How much will I need? I have a low profile TA performance rear girdle. +1/2 pint.

 

[dynoman]

I just did mine the weekend and I used Lucas HD 80W-90 non synthetic . I will put in limited slip additive as needed . Just google "turbobuick differential fluid" and you will get all the threads on this subject . Lots of different opinions on this subject , read and you decide . Do not fill up to the hole on the cover . Use the hole near the pinion for fluid level and fill through the cover . You will need about 2 1/2 qts to fill up . Sam

 

[troyk]

So I did the search & the best I come up with is "80w-90 weight GL-4", is this correct?

I've seen the wars, I think I want stock grease & not guess an answer from the war on synthetic or not & the varying weights they were using.

 

[robzombie]

It's gear oil not grease.

And to answer your question [80w-90 weight GL-4", is this correct?] .

Yes that will be fine and don't forget the posi additive.

 

[dynoman]

I just used Lucas 80W-90 gear oil , not sure of it's GL rating . GL4 is rated for use in syncromesh transmissions also and GL5 for higher pressure applications , like high HP differentials

 

[forcefed3.8's]

The limited slip additive actually makes the clutches slip so they wont make noise around corners. I use 1qt of fluid with additive and 1qt without, and have no problems.

 

[dynoman]

I went for a ride last night after fluid change . I used Lucas HD 80W-90 non-syn. & no additive . No chatter what so ever , even when backing up slow and turning full lock right & left . It says on the bottle " for limited slip , no additive needed " , so far so good .

 

[forcefed3.8's]

It alreadyhas the additive. I use that lucas oil and then the parts store special. If it makes a difference, who knows. The posi units in the gns are pretty good, i havent had a bad one yet.

 

[troyk]

I've been reading not to use GL5 in system with yellow metals, do I have yellow metals in my rear end?

 

[dynoman]

I've been reading not to use GL5 in system with yellow metals, do I have yellow metals in my rear end?

What they are talking about is using GL5 oils in synchromesh transmissions where there are "soft metals " like brass . GL4 oils have 1/2 the additives that GL5 oils have . Read this article that explains the difference . http://www.widman.biz/uploads/Transaxle_oil.pdf
And no you don't have yellow metals in the rear differential . Sam

 

[troyk]

So the GM additive I have 1052358, is it the same kind of additive as the upgrade from GL4 to GL5 is adding or is the additive upgrade from GL4 to GL5 only for higher pressure, not chatter?

If they are the same kind of additive, should I just buy GL4 & add GM additive as needed to stop the chatter? This way I know the clutches are grabbing the best they can wo/being annoying? or should I worry more about the gear stress(GL5), not the clutch slip at the track?

Lucas HD Plus, 80W90, Hypoid, GL5 has additive.
Valvoline HP 80W90, GL5 has additive.

 

[dynoman]

The difference between GL4 & GL5 has nothing to do with the additive for posi clutches . The difference between the two , is one should be used in syncromesh transmissions which have "yellow metals" & rear differentials (GL4) , the other in high power rear differentials (GL5). Some fluids have the posi additive in them already . Just put in a GL5 fluid with additive in it already and your good to go , and if it does chatter then add more additive , Mine didn't .

the additive upgrade from GL4 to GL5 only for higher pressure, not chatter?

Correct .

 

[gunzandgearz]

The best additive out there is the ford motorcraft posi additive. I use it in all the limited slip diffs I build.