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#4753712 - 05/11/18 04:04 AM 98 Ford Mustang gt rear diff
MetalSlug Offline


Registered: 07/24/10
Posts: 2630
Loc: vicksburg ms
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.
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#4753722 - 05/11/18 05:04 AM Re: 98 Ford Mustang gt rear diff [Re: MetalSlug]
Char Baby Online   content


Registered: 05/25/05
Posts: 9922
Loc: 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.
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#4753755 - 05/11/18 05:53 AM Re: 98 Ford Mustang gt rear diff [Re: Char Baby]
MetalSlug Offline


Registered: 07/24/10
Posts: 2630
Loc: vicksburg ms
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 itís start whining bad . I think the shop rebuild closer factory spec . So 75w90 Mobil 1 then . Itís just daily drive
_________________________
NO FRAM OCOD " Orange Can Of DEATH ď
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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#4753764 - 05/11/18 06:10 AM Re: 98 Ford Mustang gt rear diff [Re: MetalSlug]
Char Baby Online   content


Registered: 05/25/05
Posts: 9922
Loc: ROCHESTER, NY
IMHO, YES!
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"Retired"
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'06 Mazda 3i 2.0L
'15 Nissan Altima 2.5 SV

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#4753816 - 05/11/18 07:09 AM Re: 98 Ford Mustang gt rear diff [Re: MetalSlug]
racin4ds Offline


Registered: 05/07/10
Posts: 878
Loc: 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)
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#4753827 - 05/11/18 07:23 AM Re: 98 Ford Mustang gt rear diff [Re: MetalSlug]
Char Baby Online   content


Registered: 05/25/05
Posts: 9922
Loc: 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.
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"Retired"
'80 Firebird FORMULA V8/4bbl-purchased "NEW"
'06 Mazda 3i 2.0L
'15 Nissan Altima 2.5 SV

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#4753832 - 05/11/18 07:28 AM Re: 98 Ford Mustang gt rear diff [Re: MetalSlug]
zeng Offline


Registered: 09/01/15
Posts: 2145
Loc: Malaysia
Originally Posted By: MetalSlug
My owners manual say 80w90 . It was rebuild because itís start whining bad . I think the shop rebuild closer factory spec . So 75w90 Mobil 1 then . Itís just daily drive

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

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#4753922 - 05/11/18 08:51 AM Re: 98 Ford Mustang gt rear diff [Re: MetalSlug]
Trav Offline


Registered: 11/20/06
Posts: 18553
Loc: 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.
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#4754171 - 05/11/18 12:18 PM Re: 98 Ford Mustang gt rear diff [Re: MetalSlug]
SubieRubyRoo Offline


Registered: 05/14/12
Posts: 1017
Loc: Winchester, Indiana
Gear 300 from Motul

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#4754318 - 05/11/18 03:22 PM Re: 98 Ford Mustang gt rear diff [Re: MetalSlug]
SevenBizzos Offline


Registered: 12/10/06
Posts: 687
Loc: The IL
I put M1 75W-90 in mine. Runs as quiet as can be.

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#4754667 - 05/11/18 11:19 PM Re: 98 Ford Mustang gt rear diff [Re: MetalSlug]
MetalSlug Offline


Registered: 07/24/10
Posts: 2630
Loc: vicksburg ms
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 ď
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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