Rear End Gear Oil

[SierraMtns]

I pulled the diff cover to figure out what gears are in the rear end. I got the diff cover cleaned and ready to reinstall. What kind of gear oil should I run? I was thinking 90w synthetic with a posi additive.

[cdowns]

I like the royal purple stuff there is no need for a posi sadditive with the royal pyrple

[Fitz]

Originally Posted by SierraMtns

I pulled the diff cover to figure out what gears are in the rear end. I got the diff cover cleaned and ready to reinstall. What kind of gear oil should I run? I was thinking 90w synthetic with a posi additive.

That is an Eaton Posi unit and they are quite adamant about the type of oil to use:

"Eaton Posi units perform best when using GL4 (or better) mineral/petroleum based gear oil. A four ounce bottle of friction additive/modifier is also necessary for optimum performance."

In short, do not use synthetics. They increase the clutch wear.

[SierraMtns]

Originally Posted by Fitz

That is an Eaton Posi unit and they are quite adamant about the type of oil to use:

"Eaton Posi units perform best when using GL4 (or better) mineral/petroleum based gear oil. A four ounce bottle of friction additive/modifier is also necessary for optimum performance."

In short, do not use synthetics. They increase the clutch wear.

So dose that mean this is a Eaton rear end?

[leftybass209]

It's just the posi manufacturer. There were other manufacturers of posi units as well.

[SierraMtns]

Originally Posted by Fitz

That is an Eaton Posi unit and they are quite adamant about the type of oil to use:

"Eaton Posi units perform best when using GL4 (or better) mineral/petroleum based gear oil. A four ounce bottle of friction additive/modifier is also necessary for optimum performance."

In short, do not use synthetics. They increase the clutch wear.

Originally Posted by leftybass209

It's just the posi manufacturer. There were other manufacturers of posi units as well.

Ok thanks.

Is there a friction additive/modifier you guys would recommend?

[hugger6933]

GM used to have a posi additive I would imagine they still do

[Fitz]

Originally Posted by SierraMtns

So dose that mean this is a Eaton rear end?

No, it does not. The carrier is an Eaton Posi carrier in a GM 12 Bolt differential.

[Fitz]

Originally Posted by SierraMtns

Ok thanks.

Is there a friction additive/modifier you guys would recommend?

Sure. Either, both and many other brands available from your local auto parts store or Summit Racing!

[jayoldschool]

Yep, no syn with an Eaton. Good 80w90 and a bottle or two of the GM posi additive.

[cdowns]

Originally Posted by Fitz

That is an Eaton Posi unit and they are quite adamant about the type of oil to use:

"Eaton Posi units perform best when using GL4 (or better) mineral/petroleum based gear oil. A four ounce bottle of friction additive/modifier is also necessary for optimum performance."

In short, do not use synthetics. They increase the clutch wear.

horsecrap why does gm come loaded with mobil one synthetic on eaton posi trucks from the factory from day one

[Shaky]

Interested to see where this conversation goes.

Whatever you end up using, I would make sure it is API GL-5 rated.

[Fitz]

Originally Posted by cdowns

horsecrap why does gm come loaded with mobil one synthetic on eaton posi trucks from the factory from day one

When it comes to lube recommendations I'll take the advice of the manufacturer every time! After all, they did engineer, design, produce and sell the part!

OBTW if you check the tech support on the Eaton website they do say that synthetic oils dissolve the clutch material in their PosiTrac units shortening the life of the clutch pac.

Please note that the friction additive GM recommends is the AC Delco part number 10-4003.

[cdowns]

Why did gm put mobil one synthetic gear oul in from the factory answer that question instead of avoiding the issue

[CUSTOM/10]

Here's a link to Eatons owners manual, page 25 covers the lub specs. It does list either can be used.
Not sure if this applys to a 40+ yr old unit ?

http://www.eaton.com/ecm/idcplg?IdcS...me=PCT_1087652

[RenoKeene]

Originally Posted by cdowns

Why did gm put mobil one synthetic gear oul in from the factory answer that question instead of avoiding the issue

Mobil One was first introduced in 1974 so why do you think it was factory supplied in our 67-72 trucks?

[cdowns]

LEARN HOW TO REad as I never said it was in 67-72 chevy trucks// I had a 96 chevy with an eaton posi from the factory and it came from the factory with mobil one synthetic oil

[RenoKeene]

Originally Posted by cdowns

LEARN HOW TO REad as I never said it was in 67-72 chevy trucks// I had a 96 chevy with an eaton posi from the factory and it came from the factory with mobil one synthetic oil

So why did you post this on the 67-72 forum, did you think the OP was talking about a late model truck?

[Fitz]

Originally Posted by cdowns

Why did gm put mobil one synthetic gear oul in from the factory answer that question instead of avoiding the issue

For your 1996, GM DOES recommend synthetic oil for your differential. And, that differential does use an Eaton limited Slip center section. Your problem is you thought you had a clutche Eaton Posi unit but it is, in fact an Eaton TrueTrac which uses planetary gears not a clutch pack.

[GASoline71]

LMAO...



Gary

[Stocker]

This thread has been quite informative!!

[cdowns]

fact of the matter is that synthetic oil is far superior and causes no long term problems when used in a posi or locker of any type
back to the horsecrap statement that you can't use synthetic

[donandal]

Originally Posted by Fitz

Sure. Either, both and many other brands available from your local auto parts store or Summit Racing!

thanks Fitz,

I had my rear end rebuilt and added an Eaton posi.

The shop included a bottle of the yukon additive, and said
to just use regular gear oil, not synthetic.

They didn't say why no synthetic, but now that makes sense.

Thanks

[jayoldschool]

Originally Posted by cdowns

fact of the matter is that synthetic oil is far superior and causes no long term problems when used in a posi or locker of any type
back to the horsecrap statement that you can't use synthetic

Incorrect, and misinformation. We're not talking engine oil here. The actual manufacturer specifies no syn. That isn't enough for you? How about real-world experience from people who have ignored that advice and went with syn, experienced problems, then switched back to the recommended dino and the problems were fixed?

Just make sure it's not synthetic horsecrap, and you'll be ok.

[jayoldschool]

Originally Posted by cdowns

LEARN HOW TO REad as I never said it was in 67-72 chevy trucks// I had a 96 chevy with an eaton posi from the factory and it came from the factory with mobil one synthetic oil

Perhaps you should learn to do some reading. The 96 had the Eaton Gov-bomb mechanical locker, and that's why it used synthetic. Not an Eaton clutch posi. Don't forget the bullets at your next gunfight.