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Old 03-17-2019, 05:27 PM   #1
Davidw04
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Differential fluid

What’s everyone using? I just got some royal purple 75w90 and a bottle of fords friction modifier. Will this work or should I have gone with the 75w140?

Last edited by Davidw04; 03-17-2019 at 06:12 PM.
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Old 03-18-2019, 02:10 PM   #2
j rick kirby
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Re: Differential fluid

I use the RP 75w140 but I track the car so you're good. You won't need the friction modifier.
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Old 03-18-2019, 08:44 PM   #3
311-420
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Re: Differential fluid

The rp says it contains a friction modifier, but from my experience it wasn't enough as both of my old FR diffs would chatter pretty good in a hairpin (parking spaces, tight garage entries etc) while running straight rp 75-140.
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Old 03-19-2019, 09:03 AM   #4
j rick kirby
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Re: Differential fluid

Mine have never chattered with the straight RP.
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2003 Azure mach1 5 speed with IUP
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2012 Candy Red Metalic Premium GT with Brembo/Trak Pak and 373s
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Old 03-19-2019, 08:32 PM   #5
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Re: Differential fluid

Quote:
Originally Posted by j rick kirby View Post
Mine have never chattered with the straight RP.
Which diff are you using? My first one I used rp in was the stocker from my old 04 IRS setup. I had it rebuilt back to FR specs with new carbon discs and gears. The second one was a brand new FR piece I ran for a short while in my (now) SRA setup.
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452hp/409tq dynojet🏁
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Old 03-20-2019, 08:12 AM   #6
j rick kirby
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Re: Differential fluid

It's a FPRP 31 spline with the carbon fiber clutch pack.
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2003 Azure mach1 5 speed with IUP
Maximum Motorsports R&T Box with Torque Arm and lots of other bits and pieces here and there
2012 Candy Red Metalic Premium GT with Brembo/Trak Pak and 373s
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Old 03-20-2019, 09:08 AM   #7
gfong
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Re: Differential fluid

Just put the Ford friction stuff in along with whatever other diff oil brand you are going to use. Unless it requires non friction oil which it doesn't then adding the 4oz little bottle of Ford stuff is better in it than not in it!

Our cars and Cobras from the same years use 75W140 in the rear end.
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