Best Rear End Gear Oil

93gtmustang

10 Year Member

Oct 21, 2006

517

43

49

Mar 25, 2007

#1

• Mar 25, 2007

• #1

I have a 1993 GT Mustang. Street legal. Mostly used at the track.
New 3.73's, 31 Spline Moser Axles, Eaton Heavy Duty Posi.
What's the best gear oil to use?
Thanks

 

S

steadfastcrew

New Member

Feb 8, 2007

15

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0

North Las Vegas

Mar 25, 2007

#2

• Mar 25, 2007

• #2

i hear that redline is great.. but than again most of everyone tells me theres nothing wrong with OEM stuff..

 

Roland69

Sergeant Tangnet

Sep 17, 2005

2,867

3

58

Port Elgin, Ontario

Mar 25, 2007

#3

• Mar 25, 2007

• #3

I want to give Royal Purole a try....but right now I have QS 80W-90 with the FM

 

KDK1988GT

Founding Member

Jan 7, 2002

1,937

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37

Fredericton

Mar 25, 2007

#4

• Mar 25, 2007

• #4

I run....Mobil 1 Synthetic Gear Lubes

 

bloopbloob

Member

Sep 27, 2006

578

4

16

Alberta

Mar 25, 2007

#5

• Mar 25, 2007

• #5

sorry if i'm jacking this thread, but is there much gain (ie decreased drivetrain loss) by changing gear oil? if so, how much? or is it just for better protection?

 

Mustang78

New Member

Feb 8, 2006

486

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Aberdeen, WA

Mar 25, 2007

#6

• Mar 25, 2007

• #6

synthetic i've heard can gain for about 5hp, but that was coming from a guy that runs a high 8 sec front engine dragster...i doubt you'll feel a difference, but the only thing a quality oil will hurt is your wallet

~Mark~

 

TrophyHead

15 Year Member

Mar 18, 2003

1,195

11

49

PA

Mar 25, 2007

#7

• Mar 25, 2007

• #7

Amsoil is a pretty good name also.

 

3

331 stang91

Member

Oct 16, 2004

261

0

16

wisconsin

Mar 25, 2007

#8

• Mar 25, 2007

• #8

I use royal purple . I've tried others and would say that it seems to perform the best.

 

Roland69

Sergeant Tangnet

Sep 17, 2005

2,867

3

58

Port Elgin, Ontario

Mar 25, 2007

#9

• Mar 25, 2007

• #9

I wouldn't think you will feel anything from changing gear oil but it's just good to have clean fresh fluids...and when you have the cover off you can get rid of some metal shavings that may be in there

 

P

PRO50SC

New Member

Dec 28, 2003

1,012

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Olney, Maryland

Mar 26, 2007

#10

• Mar 26, 2007

• #10

I run RP in mine.

 

Darkwriter77

Resident Ranting Negative Nancy

5 Year Member

Jul 1, 2005

314

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134

Apache Junction, AZ

Mar 26, 2007

#11

• Mar 26, 2007

• #11

I'd say pretty much any of the synthetics would be a good way to go with rear gear fluid. It seems to hold up a lot longer over time than the old-school dino juice. No gains or anything, just longevity.

FWIW, I run Mobil 1 in my diff.

 

ronburgundy

Member

Nov 19, 2006

179

0

16

BC coast

Mar 26, 2007

#12

• Mar 26, 2007

• #12

i would say synthetics should be fine. however, when i installed my eaton posi, there was a tag in the box that said to not use synthetic oil. maybe the clutch plates don't like it? it said to use regular gear oil with the friction modifier. any eaton guys out there that know?

 

9

91notchbk

Member

Nov 20, 2006

163

1

18

Jackson Michigan

Dec 14, 2007

#13

• Dec 14, 2007

• #13

ronburgundy said:

i would say synthetics should be fine. however, when i installed my eaton posi, there was a tag in the box that said to not use synthetic oil. maybe the clutch plates don't like it? it said to use regular gear oil with the friction modifier. any eaton guys out there that know?

Click to expand...

Yes, conventional oil not synthetic. Symthetic will cause clutch chatter.

 

bloopbloob

Member

Sep 27, 2006

578

4

16

Alberta

Dec 14, 2007

#14

• Dec 14, 2007

• #14

holy crap! back from the dead!

i'm running (75-90 i think?) synthetic royal purple now, and no friction modifier, with and extra disc in my trac-lok. no problems so far, been running it about 2 months now....

 

8

87'GTstang

New Member

Feb 16, 2004

1,025

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Dec 14, 2007

#15

• Dec 14, 2007

• #15

bloopbloob said:

holy crap! back from the dead!

Click to expand...

Yeah, no kidding.

The factory stuff is hard to beat. Amsoil is some unreal stuff, I have seen it do things no other lubricant can in industry ASTM testing. Mobil is good, Royal Purple is decent, Redline is junk. For you guys running the Zexel Torsen and Eaton True-Trac, the F-series Superduty factory fill performs really well with these or any other type of mechanical differential not using friction materials (clutches, cones, ect.).

 

Blown331LX

Member

Apr 5, 2005

227

0

16

Chapel Hill, NC

Dec 14, 2007

#16

• Dec 14, 2007

• #16

Personally I run a mix of honey, silly putty, bourbon and mustard. I have no gear whine and great traction. Only down fall is if your ridding behind me it smells like none other............... JK .........................I run Mobil 1 75w140 synthetic with friction modifer from Ford. Dont use any gear oil synthetic or non without the friction modifier. The FM is that nasty god aweful smelling blue **** in the 4 oz bottle. Dont get it on your hands, youll never get that stench out. Anyway AMSOIL and MOBIL make the best lubricants, use one of those and swing by the Ford dealer and grab a 4oz bottle of whale sperm.

 

bloopbloob

Member

Sep 27, 2006

578

4

16

Alberta

Dec 14, 2007

#17

• Dec 14, 2007

• #17

fabfordtech said:

Personally I run a mix of honey, silly putty, bourbon and mustard. I have no gear whine and great traction. Only down fall is if your ridding behind me it smells like none other............... JK .........................I run Mobil 1 75w140 synthetic with friction modifer from Ford. Dont use any gear oil synthetic or non without the friction modifier. The FM is that nasty god aweful smelling blue **** in the 4 oz bottle. Dont get it on your hands, youll never get that stench out. Anyway AMSOIL and MOBIL make the best lubricants, use one of those and swing by the Ford dealer and grab a 4oz bottle of whale sperm.

Click to expand...

Well from what i've learned so far, thats not always true. you want to run as little friction modifier as possible, as long as you don't get chatter. The royal purple has some sort of friction additive already in it. I had my gears installed by a mechanic that ONLY does performance ford work. nothing else, for the last 17 years & its mostly on mustangs. he recommended not to use the modifier, and i trust his work. i've heard the same before around here a couple times also.
no chatter so far, no more 1 wheel peels, and hooks dead straight. no complaints.

 

cobradvm

New Member

Sep 2, 2003

245

1

0

Woodinville, WA

Dec 15, 2007

#18

• Dec 15, 2007

• #18

Redline synthetic with no FM here - works great.

 

93gtmustang

10 Year Member

Oct 21, 2006

517

43

49

Feb 19, 2008

#19

• Feb 19, 2008

• #19

I talked to Eaton tech today.
They do not reccomend synthetic gear oil with their posi units.
Coventional 80w-90 for the North Eastern part of the states.
Also, get the friction modifier from a Ford dealer. There is one that has a sea green color, that's the best one to get. And there is another that is an orange color, either one will work but the green one is the best I was told.
Fill 1/2 way with gear oil. then add 4oz friction modofier, then fill the rest with gear oil untill it flows out of the fill hole.
Clutch chatter when cornering after a drain is normal because the clutches are not fully lubed.
Go to a parking lot and do several figure 8's in each direction and that should get rid of any chatter.
This is what I was told at Eaton.
I thought I'd pass the information on to everyone.

 

Taz92gt

Member

Oct 4, 2006

54

1

8

Knoxville Tn

Feb 19, 2008

#20

• Feb 19, 2008

• #20

I used Lucas in mine and you don't need a friction modifier either. I havent had any problems with it.