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98 Ford Mustang gt rear diff #4753712
05/11/18 04:04 AM
05/11/18 04:04 AM
Joined: Jul 2010
Posts: 2,653
Dallas TX
MetalSlug Offline OP
MetalSlug  Offline OP
Joined: Jul 2010
Posts: 2,653
Dallas TX
I got the rear diff rebuild 3000 miles ago . The builder running some OREILLY 80w90 . I want to flush it and change to synthetic . I think the factory call for 75w90 . But dint ford switch over to 75w140 on all their 8.8 diff ? Thanks

My fluid choice either Mobil 1 or valvoline . Just need to know which weight.


NO FRAM OCOD " Orange Can Of DEATH �
03 SVT COBRA 10th anniversary Whipple 600whp M1 5w30 Wix 51372XP
01 Corvette ZO6 stock M1 5w30 / M1-107A
2016 NISSAN TITAN dealer OC daily drive
Re: 98 Ford Mustang gt rear diff [Re: MetalSlug] #4753722
05/11/18 05:04 AM
05/11/18 05:04 AM
Joined: May 2005
Posts: 10,390
ROCHESTER, NY
Char Baby Offline
Char Baby  Offline
Joined: May 2005
Posts: 10,390
ROCHESTER, NY
Do you have an owner's manual?
Was the Diff rebuilt to factory spec's or was it BUILT?
Are you going to TRACK the car(1/4 mi or OVAL Track)?
Does the Diff have LSD?

Nothing wrong with 75w90 or 80w90 for the street. Mobil 1 is my choice however, others will chime in with more info.


"Retired"
-----------------------------------

'80 Firebird FORMULA V8/4bbl-purchased "NEW"
'15 Nissan Altima 2.5 SV
'15 Honda Civic LX
Re: 98 Ford Mustang gt rear diff [Re: Char Baby] #4753755
05/11/18 05:53 AM
05/11/18 05:53 AM
Joined: Jul 2010
Posts: 2,653
Dallas TX
MetalSlug Offline OP
MetalSlug  Offline OP
Joined: Jul 2010
Posts: 2,653
Dallas TX
Originally Posted By: Char Baby
Do you have an owner's manual?
Was the Diff rebuilt to factory spec's or was it BUILT?
Are you going to TRACK the car(1/4 mi or OVAL Track)?
Does the Diff have LSD?

Nothing wrong with 75w90 or 80w90 for the street. Mobil 1 is my choice however, others will chime in with more info.


My owners manual say 80w90 . It was rebuild because its start whining bad . I think the shop rebuild closer factory spec . So 75w90 Mobil 1 then . Its just daily drive


NO FRAM OCOD " Orange Can Of DEATH �
03 SVT COBRA 10th anniversary Whipple 600whp M1 5w30 Wix 51372XP
01 Corvette ZO6 stock M1 5w30 / M1-107A
2016 NISSAN TITAN dealer OC daily drive
Re: 98 Ford Mustang gt rear diff [Re: MetalSlug] #4753764
05/11/18 06:10 AM
05/11/18 06:10 AM
Joined: May 2005
Posts: 10,390
ROCHESTER, NY
Char Baby Offline
Char Baby  Offline
Joined: May 2005
Posts: 10,390
ROCHESTER, NY
IMHO, YES!


"Retired"
-----------------------------------

'80 Firebird FORMULA V8/4bbl-purchased "NEW"
'15 Nissan Altima 2.5 SV
'15 Honda Civic LX
Re: 98 Ford Mustang gt rear diff [Re: MetalSlug] #4753816
05/11/18 07:09 AM
05/11/18 07:09 AM
Joined: May 2010
Posts: 1,094
Ocala, Florida
racin4ds Offline
racin4ds  Offline
Joined: May 2010
Posts: 1,094
Ocala, Florida
Either will work fine. Ford did back spec many 8.8's to use the 75W140 syn fluids but I've never had an issue with 80W90 in any of my previous stangs.

Don't forget the friction modifier additive if you have the factory clutch pack locker (tracloc)


Just say NO to thin oils and M1!
05 F350 Powerstroke
05 Hyundai Tucson
08 Legacy GT
Re: 98 Ford Mustang gt rear diff [Re: MetalSlug] #4753827
05/11/18 07:23 AM
05/11/18 07:23 AM
Joined: May 2005
Posts: 10,390
ROCHESTER, NY
Char Baby Offline
Char Baby  Offline
Joined: May 2005
Posts: 10,390
ROCHESTER, NY
The Mobil 1 75W90 has the LSD additive in it already.

Just an FYI,
Funny thing I've read, many folks don't seem like synthetic gear lubes for one reason or another. There are some dino gear lubes(in which I use) that also have the LSD add in them such as PEAK 80W90 LSD from Pep Boys for about $15-$16 gal rather than $11-$12 qt for the M1...just saying as, IDK if a rebuilt Diff needs to be broken-in but if so, dino gear lube may be an alternative for several drain & fill for this process before using a synthetic.


"Retired"
-----------------------------------

'80 Firebird FORMULA V8/4bbl-purchased "NEW"
'15 Nissan Altima 2.5 SV
'15 Honda Civic LX
Re: 98 Ford Mustang gt rear diff [Re: MetalSlug] #4753832
05/11/18 07:28 AM
05/11/18 07:28 AM
Joined: Sep 2015
Posts: 2,338
Malaysia
zeng Offline
zeng  Offline
Joined: Sep 2015
Posts: 2,338
Malaysia
Originally Posted By: MetalSlug
My owners manual say 80w90 . It was rebuild because its start whining bad . I think the shop rebuild closer factory spec . So 75w90 Mobil 1 then . Its just daily drive

Checking with you ,did you use 75W90 regularly prior to rebuild ?

Re: 98 Ford Mustang gt rear diff [Re: MetalSlug] #4753922
05/11/18 08:51 AM
05/11/18 08:51 AM
Joined: Nov 2006
Posts: 20,128
MA, Mittelfranken.de
Trav Offline
Trav  Offline
Joined: Nov 2006
Posts: 20,128
MA, Mittelfranken.de
Ford seems to like the 75w140 in their larger diffs it works well even in cold parts of the country. I use Mobil 1 with Ford stink additive.


ASE L1, Master. Deutsch Meisterbrief.
Re: 98 Ford Mustang gt rear diff [Re: MetalSlug] #4754171
05/11/18 12:18 PM
05/11/18 12:18 PM
Joined: May 2012
Posts: 1,591
The land of USA-made Subies!
SubieRubyRoo Online content
SubieRubyRoo  Online Content
Joined: May 2012
Posts: 1,591
The land of USA-made Subies!
Gear 300 from Motul

Re: 98 Ford Mustang gt rear diff [Re: MetalSlug] #4754318
05/11/18 03:22 PM
05/11/18 03:22 PM
Joined: Dec 2006
Posts: 745
The IL
SevenBizzos Offline
SevenBizzos  Offline
Joined: Dec 2006
Posts: 745
The IL
I put M1 75W-90 in mine. Runs as quiet as can be.

Re: 98 Ford Mustang gt rear diff [Re: MetalSlug] #4754667
05/11/18 11:19 PM
05/11/18 11:19 PM
Joined: Jul 2010
Posts: 2,653
Dallas TX
MetalSlug Offline OP
MetalSlug  Offline OP
Joined: Jul 2010
Posts: 2,653
Dallas TX
pick up 2 quart of M1 75w90 at auto zone, and a bottle of tranx. I guess this stay in there for good.thank you guys,


NO FRAM OCOD " Orange Can Of DEATH �
03 SVT COBRA 10th anniversary Whipple 600whp M1 5w30 Wix 51372XP
01 Corvette ZO6 stock M1 5w30 / M1-107A
2016 NISSAN TITAN dealer OC daily drive

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