17 Mustang GT

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Differential has 75w85 in it. Cars prior to 2015 had 75w140 in the solid axles. New cars are IRS. I doubt the thin gear oil was for nothing more than helping meet CAFE requirements. I'm about ready to change the oil to 75w110 Amsoil Severe Gear.

Does anyone here have good experience putting Severe Gear in a Ford LSD without using the Ford LSD additive?
 
I'd think you would need to add the LSD additive unless the oil says it already has the proper additive for LSD.
 
Valvoline 75W140 said it had the additive, but the Explorer made a light rubbing noise in turns. I added the additive and it got quiet. If it says it has the additive, listen for any noise, you can always add it.
 
Originally Posted By: Anthony
Differential has 75w85 in it. Cars prior to 2015 had 75w140 in the solid axles. New cars are IRS. I doubt the thin gear oil was for nothing more than helping meet CAFE requirements. I'm about ready to change the oil to 75w110 Amsoil Severe Gear.

Does anyone here have good experience putting Severe Gear in a Ford LSD without using the Ford LSD additive?


I keep promising myself not to get dragged into high vis versus low vis discussions but consider for a moment that the supplier of the Gear set for the IFS is not related to the supplier of the gear case for the solid axle. Maybe phone them up and discuss it with them.
 
Originally Posted By: Anthony
Differential has 75w85 in it. Cars prior to 2015 had 75w140 in the solid axles. New cars are IRS. I doubt the thin gear oil was for nothing more than helping meet CAFE requirements. I'm about ready to change the oil to 75w110 Amsoil Severe Gear.

Does anyone here have good experience putting Severe Gear in a Ford LSD without using the Ford LSD additive?


I have always needed FM in my clutch type LSD's. Mostly FOrd trac-lok but also my Eaton Posi. YMMV.
 
Originally Posted By: bdcardinal
If it has a Torsen, which some do, you do not need an LS additive.


Are they still using the Trac Loks in some of the new IRS diffs?
(The Track Pack/Performance Pack options use the T2R Torsen exclusively, correct?)
 
FWIW my IRS in my Challenger calls for 75W-90 oil and I had a groaning/rubbing noise when I first got the car. It sounded like tires rubbing when I went around a sharp low-speed turn except more muffled. I drained out the oil, added the additive (I think it was 4 oz. Lubegard) and filled it up w/75W-90 Valvoline synthetic gear oil and the noise went away. I remember it didn't take much oil to fill it. My 2010 V-6 IRS Challenger called for 75W-140 while the same year V-8 Challengers called for 75W-90. I would use what the mfg recommends. The oil that came out of my Challenger looked good and had 10,000 miles on it, but I wanted to actually look at it instead of just add the additive to the oil already there. I don't know the history of the car as I bought it used w/7,500 miles, so it might have 7,500 quarter miles on it AFAIK.
 
Originally Posted By: dailydriver
Originally Posted By: bdcardinal
If it has a Torsen, which some do, you do not need an LS additive.


Are they still using the Trac Loks in some of the new IRS diffs?
(The Track Pack/Performance Pack options use the T2R Torsen exclusively, correct?)


Yes, if it has another gear ratio besides 3.73 then it is a clutch type. And it is a T2, not a T2R unfortunately.
 
Originally Posted By: bdcardinal
Originally Posted By: dailydriver
Originally Posted By: bdcardinal
If it has a Torsen, which some do, you do not need an LS additive.


Are they still using the Trac Loks in some of the new IRS diffs?
(The Track Pack/Performance Pack options use the T2R Torsen exclusively, correct?)


Yes, if it has another gear ratio besides 3.73 then it is a clutch type. And it is a T2, not a T2R unfortunately.


I certainly HOPE it is a T2R in the GT350s/350Rs? (They really NEED that diff!)
 
Originally Posted By: bdcardinal
Originally Posted By: dailydriver
Originally Posted By: bdcardinal
If it has a Torsen, which some do, you do not need an LS additive.


Are they still using the Trac Loks in some of the new IRS diffs?
(The Track Pack/Performance Pack options use the T2R Torsen exclusively, correct?)


Yes, if it has another gear ratio besides 3.73 then it is a clutch type. And it is a T2, not a T2R unfortunately.


I certainly HOPE that the GT350s/350Rs have the T2R in their center pumpkin, as those monsters NEED that diff in a serious way!
wink.gif
 
There isn't a correct viscosity grade for any particular unit of transmission/differential component.
Use 75W85 for maximum fuel economy(?) on one 'extreme'.
Use 75W140 for maximum components protection on the other 'extreme'.
Use 75W90 or 75W110 for optimum(or compromised) fuel economy, or components protection.
It's application-dependent or individual priority , really.
 
I’m running Motorcraft 75w140 with bottle of FORD lsd addi . Since it’s so difficult to change rear diff fluid on my 03 cobra terminator . Because the whole irs need to be drop. I don’t think i ever need to change it again. Run smooth . Side note “ I should add a aftermarket cover with drain and fill plug for easy change . But I couldn’t see myself add another $300 for the cover on top of $700 I just pay for since the dealer drop it and add new bushing and stuff. That is the most expensive rear diff fluid I ever pay for
 
Installed the Amsoil 75w110 Severe Gear a couple of days ago. I did not use any friction modifier. So far so good. Car has 8400 miles on it.

I also installed BG Synchro Shift 75w80 GL4 into the transmission. Car comes from factory with Ford Dual Clutch fluid. I haven't noticed much of a difference, but my Transmission has always felt fine so no complaints there.
 
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