Rear End Gear Oil - The 1947 - Present Chevrolet & GMC Truck Message Board Network

SierraMtns · 10-13-2015, 04:15 PM

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 · 10-13-2015, 04:25 PM

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

*Fitz* · 10-13-2015, 04:59 PM

Quote:

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 · 10-13-2015, 05:33 PM

Quote:

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 · 10-13-2015, 05:39 PM

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

SierraMtns · 10-13-2015, 05:50 PM

Quote:

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.

Quote:

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?

*Fitz* · 10-13-2015, 07:11 PM

Quote:

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!

*Fitz* · 10-13-2015, 07:09 PM

Quote:

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.

cdowns · 10-13-2015, 09:48 PM

Quote:

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

*Fitz* · 10-14-2015, 11:42 AM

Quote:

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 · 10-14-2015, 12:39 PM

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

**CUSTOM/10** · 10-14-2015, 01:13 PM

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** · 10-14-2015, 01:39 PM

Quote:

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?

*Fitz* · 10-14-2015, 04:12 PM

Quote:

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.

hugger6933 · 10-13-2015, 06:08 PM

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

Shaky · 10-14-2015, 06:07 AM

Interested to see where this conversation goes.

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

GASoline71 · 10-14-2015, 04:31 PM

LMAO...

Gary

cdowns · 10-14-2015, 05:27 PM

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

**jayoldschool** · 10-14-2015, 07:46 PM

Quote:

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.

**Stocker** · 10-14-2015, 05:26 PM

This thread has been quite informative!!

SierraMtns · 10-17-2015, 03:05 PM

Anyone use this stuff?

Also I am assuming LS additive is not needed since it says its for LS.

10-13-2015, 04:15 PM	#1
SierraMtns Registered User Join Date: Jun 2014 Location: Shingle Springs, CA Posts: 869	Rear End Gear Oil 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.

10-13-2015, 04:25 PM	#2
cdowns Senior Member Join Date: Jan 2003 Location: daytonabeach Posts: 22,956	Re: Rear End Gear Oil I like the royal purple stuff there is no need for a posi sadditive with the royal pyrple __________________ 71c-10 350/2004r/4:11 lowered3/4 longbed/dead by hurricane MEANING OF DEATH::::: SOMEBODY ELSE GETS YOUR STUFF DONT BELIEVE EVERYTHING YOU THINK TAKE MY ADVISE;I DON'T USE IT ANYWAY

10-13-2015, 05:39 PM	#5
leftybass209 Registered User Join Date: Feb 2011 Location: Modesto, CA Posts: 2,189	Re: Rear End Gear Oil It's just the posi manufacturer. There were other manufacturers of posi units as well.

10-14-2015, 12:39 PM	#11
cdowns Senior Member Join Date: Jan 2003 Location: daytonabeach Posts: 22,956	Re: Rear End Gear Oil Why did gm put mobil one synthetic gear oul in from the factory answer that question instead of avoiding the issue __________________ 71c-10 350/2004r/4:11 lowered3/4 longbed/dead by hurricane MEANING OF DEATH::::: SOMEBODY ELSE GETS YOUR STUFF DONT BELIEVE EVERYTHING YOU THINK TAKE MY ADVISE;I DON'T USE IT ANYWAY

10-14-2015, 01:13 PM	#12
CUSTOM/10 Senior Member Join Date: May 2003 Location: Sandown, NH Posts: 2,857	Re: Rear End Gear Oil 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 __________________ Gary 72 SWB 4x4 My 72 SWB Build http://67-72chevytrucks.com/vboard/s...d.php?t=259859

10-13-2015, 06:08 PM	#15
hugger6933 Registered User Join Date: Oct 2008 Location: Marianna Arkansas Posts: 7,280	Re: Rear End Gear Oil GM used to have a posi additive I would imagine they still do

10-14-2015, 06:07 AM	#16
Shaky Six in a row makes it go... Join Date: Mar 2009 Location: Vacationland: Maine Posts: 1,346	Re: Rear End Gear Oil Interested to see where this conversation goes. Whatever you end up using, I would make sure it is API GL-5 rated. __________________ 67 C20 long step resto: http://67-72chevytrucks.com/vboard/s...d.php?t=342086 66 C10 long step build: http://67-72chevytrucks.com/vboard/s...=1#post3814790 CT to Alaska in a 67 C10: http://67-72chevytrucks.com/vboard/s...d.php?t=399224 “The height of sophistication is simplicity." - Clare Boothe Luce

10-14-2015, 05:27 PM	#18
cdowns Senior Member Join Date: Jan 2003 Location: daytonabeach Posts: 22,956	Re: Rear End Gear Oil 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 __________________ 71c-10 350/2004r/4:11 lowered3/4 longbed/dead by hurricane MEANING OF DEATH::::: SOMEBODY ELSE GETS YOUR STUFF DONT BELIEVE EVERYTHING YOU THINK TAKE MY ADVISE;I DON'T USE IT ANYWAY

10-14-2015, 05:26 PM	#20
Stocker 20' Daredevil (Ret) Join Date: May 2003 Location: Jefferson State Posts: 13,750	Re: Rear End Gear Oil This thread has been quite informative!! __________________ - Mike - 1972 K20 LWB 350/350/205 RIP El Jay

10-17-2015, 03:05 PM	#21
SierraMtns Registered User Join Date: Jun 2014 Location: Shingle Springs, CA Posts: 869	Re: Rear End Gear Oil Anyone use this stuff? Also I am assuming LS additive is not needed since it says its for LS.



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