Deacon Don

Will it damage the rear differential if too much positrack additive is added to the lube? A friend changed mine when I wasn't there and was unaware that it required only 4 oz and he put in the whole bottle. Do I need to change it again and add the correct amount of additive?

Thanks.

Chromie69

The additive is for the posi unit..if the bottle of additive came from GM they are not much more than that..I put the whole bottle in mine..you don't get all of it out of the bottle anyhow so I wouldn't worry about it..what type of fluid..GL 5 did you put in..some already have some friction modifiers in them..

Deacon Don

Got the lube and additive from Auto Zone...can't remember at the moment the brand, but I know the bottle of additive was well over 4 oz. I'm thinking it was probably a 16 oz bottle.

Rebelrob

Yes that is correct, the posi additive is a small bottle 4-6 ounces max. That is all you need.
Just one bottle.

Deacon Don

But will it damage anything if twice that amount or more was added?

Chromie69

I would probably suck that out..the rear diff only holds a quart or so..it may not have enough GL5 in it..unless the additive was both oil and additive..you'll have to check the bottle..

Deacon Don

That's what I was thinking. I'll change it out. Better safe than sorry...

Thanks

bashcraft

AFAIK the additive doesn't come in 16 oz. bottles. He probably used GL-5 gear lube which is perfectly fine for the diff. It's gear lube with the additive already added.

tracdogg2

No it won't hurt anything. If he used GM gear lube one bottle is sufficient. If he used non-GM lube then more then one bottle is needed. The additive is only a friction modifier for the clutches.
Mike

Chromie69

Your right the additive doesn't but the mix does..

Deacon Don

Thanks fellas.

So if I use a GL-5 gear lube I don't need an additive? If so, I'll probably suck some of what's in it out and replace it with GL-5 and be done with it and have peace of mind.

bashcraft

That's what I've been running forever. Never had a problem.

Chromie69

Check your bottle Don..if it has both the additive and GL 5 your fine..

Deacon Don

Thanks. Will do.

tracdogg2

If you run the GL-5 gear lube you need one 4 oz bottle of additive. GL-5 lube has some additive in it. If it is not GL-5 or some off brand like most repair shops use you may need up to 2 bottles. The clutches will tell you have much you need. 8 oz of GM additive won't hurt anything. It has it's own lubricating properties. Too little is far worse than too much.

jb78L-82

I have used Mobil 1 GL-5 synthetic 75W-90 since 1990 (changed it twice) with no GM additive and the diff has been fine, no shuttering/Chatter, posi unit works perfectly. I would not worry about it either but I also would only use the additive if you are running a conventional diff oil.

Rally68

The stuff from Autozone is likely Trans-X, and it comes in 7 oz tubes. There is absolutely nothing wrong with adding a whole bottle of this stuff to your diff. You can pump it out if you want (only you can put a price on your peace of mind) but I'd drive it for a while first and see if it exhibits any slipping, noise or other issues.

Deacon Don

The car's being restored and the diff lube was changed some time back. I was having a difficult time remembering how big the bottle was and it has been bothering me the closer I get to finishing the car. All I could remember was that when I got to the shop one day the entire bottle had been emptied. I have driven the car in my neighborhood just a little and noticed no popping/slipping, etc, from the rear end. If there was a problem, should I have noticed it pretty quickly?

I'm gonna run by Auto Zone and see what I bought. If you're correct, I'll drive it and not worry.

Thanks!

tracdogg2

You'll only notice it if you don't have enough additive.

Vette5.5

Not much a fan of oil additive's myself, and usually just use the proper lube to begin with. Done a few diff build's like this with little problem. Some people complain of posi clutch pack chatter and dump this stuff in. Maybe help's the noise, but most of the posi action's usually gone too. Guess I'm from a school the lube manufactures got it right, and adding more stuff just messes up the engineered chemistry. If you put in to much additive, probably good to start over, and flush out the clutch pack's while you're at it.