[Formulabruce]

Toss in the 85-90 weight oil. If you REALLY want to add something, add a couple ounces of "Motorkote" to really protect the gears and bearings.
AUBURN style "posi " doesn't need any posi anti chatter lube as its 2 metal cones , no friction material like a Eaton unit.

[Greg Reid]

https://www.autozone.com/greases-and...art/693858_0_0
I think I recall using this in the past.

[SR-71]

As long as it's GL-4 you're fine if it's GL-5 then NO.

[Schurkey]

Originally Posted by Greg Reid

Cone type clutch pack?

You used a question mark. Are you asking a question or providing a statement?

Originally Posted by Greg Reid

I already have the limited slip additive, ACDelco type. Do I not need it? Assuming it wouldn't hurt to use it since I have it?

"Most" gear lubes have friction modifier for "posi" axles already mixed-in. A guy has to look around and read labels to find one that doesn't. What does the manufacturer of your differential recommend?

Even if they suggest using friction modifier, what's already in the gear lube you buy may be enough. If not, you can always add more from a small bottle of concentrate, later.

[SR-71]

To understand why you need to use a particular lube GL-4 vs GL-5 you first need to know how the "posi" unit works. If it is a clutch type unit with friction material like your transmission clutch it needs the posi lube to function properly. If it is a cone style unit it has bronze material like the bushings in your Muncie transmission has must use GL-4 as it is not compatible with GL-5 and will corrode. Some will argue that they have used GL-5 for years and never had problems. I trust the engineers that say not to use GL-5.

[Greg Reid]

Thanks, I was asking questions and not making statements... Since posting I have found the answers in the DM shop manual. I have a cone type limited slip unit as only the big cars use the clutch pack type according to the manual.
The manual recommends no additives that I could find for either type.
I did not see these responses while I was out today and of course grabbed the wrong kind. I will have to exchange it for something rated GL4.
Thanks again.

[mgarblik]

Limited slip additive will render the cone style limited slip unit you have less effective as a limited slip. IE, it will make it smoother and make it slip a little more. For maximum "limited slip" effect, don't use the additive.

[AG]

Originally Posted by SR-71

To understand why you need to use a particular lube GL-4 vs GL-5 you first need to know how the "posi" unit works. If it is a clutch type unit with friction material like your transmission clutch it needs the posi lube to function properly. If it is a cone style unit it has bronze material like the bushings in your Muncie transmission has must use GL-4 as it is not compatible with GL-5 and will corrode. Some will argue that they have used GL-5 for years and never had problems. I trust the engineers that say not to use GL-5.

There are no bronze type materials in a cone style posi like a Muncie transmission whether it is stock or an Auburn posi.

[Greg Reid]

I just read this- https://www.rymax-lubricants.com/upd...gl-4-and-gl-5/. Which confirms the bronze and/or brass members being the issue with using GL-5.. it concludes by saying that it's okay to use in a differential but not in a gearbox. Sound correct?
Not doubting AG but can anyone double down on the fact that there are no brass or bronze parts in the differential?

[Sirrotica]

Originally Posted by Greg Reid

I just read this- https://www.rymax-lubricants.com/upd...gl-4-and-gl-5/. Which confirms the bronze and/or brass members being the issue with using GL-5.. it concludes by saying that it's okay to use in a differential but not in a gearbox. Sound correct?
Not doubting AG but can anyone double down on the fact that there are no brass or bronze parts in the differential?

Greg, if the parts are all GM inside I've never seen any bronze or brass in any 10 bolts I've worked on. I can't say for certain if someone had an aftermarket posi carrier, but I can't see any reason that the aftermarket would use brass or bronze in their unit.

Way back in this thread there was a reference to using STP in the mix. Many years ago before there was all the newer additives, whenever I rebuilt a manual transmission it was common to mix STP in the new fluid after the rebuild. Because STP is so slippery it improves the shifting quite a bit over just regular gear oil. It was also said to add life to the syncro rings. The rebuilder that said add 15 ounces of STP in his race prepped differential must have wanted the added ability that STP makes everything slip more. With a hypoid gear cut, I can see his reasoning to want to make the gear faces slide easier, decreasing friction.

The STP container makes reference to using a certain percentage of STP in gear driven units for added protection, I believe it was 20% from memory. You may want to check on the container to verify my memory banks if you decide to use any STP in the refill. I don't see any negative effects on adding STP to the refill fluid.

[Greg Reid]

Thanks Brad. It looks stock to me... just like any other I've had open but I've never rebuilt one and didn't know if there was anything out of view that I didn't know about.
Now I'm worried about the Muncie I changed the oil in six or seven years ago. I have no idea what I used back then. The car has been sitting for years. I changed the oil because it had water in it.

[lust4speed]

Since there was no internet to guide me fifty plus years ago, I have always added posi additive to my '67 10-bolt posi's. I can testify that even with all these years of perpetuating that error the rearend has always laid down two even black lines down the street. Also seems to me that I remember the cone clutches grabbing around corners when I didn't use gear oil with the additive, but that was a long time ago before I switched to using Vavaline that says on the bottle it is for posi units.

[Greg Reid]

Originally Posted by lust4speed

Since there was no internet to guide me fifty plus years ago, I have always added posi additive to my '67 10-bolt posi's...... Also seems to me that I remember the cone clutches grabbing around corners when I didn't use gear oil with the additive...

I had the same problem with a 74 trans am and I seem to recall that the cure was the additive. Been about 15 years ago and that's a bit outside of my sharp memory range...lol

[Formulas]

The posi additive is a friction modifier. It changes friction,

It makes metallic parts slip smoothly past each other easier instead of stop and go jerking chattering , posi clutches or cones

GL5 has this in it already that's why you dont have to put additive in it and its approved for posi use as is

GL4 does not have this feature that's why when you use GL4 you need additive for a posi

With that said this additive in GL5 is what old school muncie transmission do not like. WHY

It's the job of the synchro's that use friction to to get the next gear selection up to speed to mesh correctly the Gl5 friction modifier renders the syncros less effective. A little friction in the right place is a good thing

[Greg Reid]

Thanks everyone. I feel comfortable using the GL-5 in the rear at this point. I'll hold off on the additive unless a chattering problem arises and at that point I would try the additive before doing anything else.

[Sirrotica]

Just to add one more point of view, in the past I have used straight gear oil that was said to already have the posi additive in from the refinery. But upon driving the car it chattered going around corners. The cure was the GM additive, and it cured the chatter.

Whether they don't use enough in their mixture, or the GM (whale oil, late 70s) was better I'm not sure.

Jeeps with quadra track, have the same type of posi differential in the transfer case with cone clutches. If you didn't use the additive it was practically impossible to put up with the chatter when you turned a corner. Just my own experiences, YMMV.

[77 TRASHCAN]

When I bought my TA, brand new...the rear end started making a snapping noise going around corners, not long after I bought it...
Took it to the dealer. They said something along the line, that the factory oil either didn't get the additive, or the oil was something that wasn't working out. I got the new oil with additive. The car drove perfectly after I got it back.

I buy 80W90 oil, any name brand ( I used to buy the GM oil, not sure if it's anything different)and one bottle of GM additive. It usually take 2-1/2 quarts of oil.

When it's getting close to full, I put my finger over the bottom of the fill hole, and cram a little extra oil in, and then install the plug.

Greg the additive won't hurt anything, if it's not needed. I use it!!!

[chiphead]

I know this is an old thread, but was looking for this info for my '67 posi rear end. Also found this tech article, full of good info:

https://www.widman.biz/uploads/Transaxle_oil.pdf

[propuckstopper]

Both of these products have worked great in my cars. The transmission fluid has really made a difference in shift quality over the Sta-Lube I was previously using.

[25stevem]

Is this the original rear in your car