Diff Oil/Friction Modifier?

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Sep 17, 2009 | 07:33 PM

dwild

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Trailering

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Diff Oil/Friction Modifier?

Hi

I have a 2003 F-150 4x4/FX4 Offroad (3:73 LSD). I want to change the diff oil. The only question I have is:

Do I need the 4 oz of friction modifier from ford despite the fact that the oil I will use
(Mobil1 LS 75w-140) already has friction modifier in it?

I love this truck

Thanks
Dwild

Sep 17, 2009 | 08:23 PM

torkum

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Joined: Dec 2005

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From: Mount Juliet, TN

Think the friction modifier is pre synthetic gear oil. You should be ok without it.

Sep 18, 2009 | 07:40 AM

dwild

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Trailering

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Friction Modifier

Thanks Torkum

Sep 18, 2009 | 09:05 AM

steve(ill)

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if you have any trouble with the LS clutch squacking, add some of the modifier. I put Full synthetic lube in the axle, and add a 7 oz tube from Auto Zone every time i change the lube.

Sep 20, 2009 | 06:09 AM

96f150

Fleet Mechanic

Joined: Nov 2000

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From: In my House

I'll second what Steve said....I had to do that with my 01 to stop it from chattering....even thought the book only says 4oz, i ended up addding about 7oz
Rich

Sep 22, 2009 | 07:43 PM

dwild

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Trailering

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Rear Diff Oil/Friction Modifiers

This is what I decided to do. I bought the 4oz bottle of motorcraft stuff (but I am not using it), and I also went with Redline 75W/140 GL5 with friction modifiers. My rear diff is not making any noise now at 101K, so if it stays quiet can we deduce we don't need the 4oz of friction modifier, right? Has anyone gone this route??

This stuff really quieted down the LSD in my 1988 BMW 325IS, which was noisy at 88K.

Dwild

2003 F-150 4x4 FX4 Offroad

Sep 22, 2009 | 07:58 PM

Mustang6147

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Friction modifiers arent needed with high end synthetice like redline, mobil1 ect. Other rear end lube it is required because of the clutch material and rear gear lube, not being slippery enough.

The rear clutches slip, thus unlocking for cornering, or under acceleration, When gear lube, isnt slippery enough as the clutches slip, they grab and slip rapidly, that is the chattering sound, or the feeling you might get.