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Friction modifer?

Discussion in 'Ford Trucks' started by MickiRig1, Sep 27, 2008.

  1. MickiRig1

    MickiRig1 PlowSite Veteran
    Messages: 3,617

    What is this " Friction Modifier " that Ford wants you to add to the differential?
    It's bad enough it calls for synthetic gear oil. The Mobil One stuff is $16.99 a quart !
  2. 84deisel

    84deisel Senior Member
    Messages: 697

    if you have a limited slip differential, the friction modifiers provide some grip for the limited slip clutches. If you dont use the modifier, your rear end will begin to chatter and you will destroy the limited slip unit.
  3. JD Dave

    JD Dave PlowSite Fanatic
    Messages: 11,194

    Yeah , I wondered too, but it's cheap insurance.
  4. mike psd

    mike psd PlowSite.com Addict
    from pa
    Messages: 1,028

    OEM additive

    if use it don't get a too big of a smell of it its nasty stuff .
  5. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    Helpful tip:

    If your running a 9 3/4, 10 1/4 or 10.5 be sure to add TWO bottles if the friction modifier due to the larger axle's fluid capacity. One bottle isn't enough in 4 qts of gear oil and will lead to shuttering in corners.
  6. MickiRig1

    MickiRig1 PlowSite Veteran
    Messages: 3,617

    Who would think there are 2 covers that are 12 bolt and the same shape. I picked the wrong one the first time!
    It's a normal open diff, BUT, it does not say just for posi rear ends. I just installed a chrome cover and put 140 synthetic grease in it. ALL of the older manuals I have state just the posi rear ends need it. IT SEEMS ok, no noise, I put 20 miles on it highway and city.
    I evan spent 20 minutes driving around on farm field I own in 4X4 and no noise's.
    Last edited: Sep 28, 2008
  7. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    Happens quite often Micki, the 9 3/4 and the 10.25/10.5 covers are ALMOST the same...so close that if you dont have them both right there side by side you can't tell them apart.

    You only need the friction modifier for a limited slip diff, so your good to go there. :drinkup:
  8. MickiRig1

    MickiRig1 PlowSite Veteran
    Messages: 3,617

    That's funny you should say they look they same. Who would think that there are two 12 bolt rear ends that year? That are the same shape and bolt count.I got the 9.75 cover, held it up with the drop light in one hand the cover in the other. It lined up in the one edge. Went to bolt it up. HELLO, there is a 1/2 inch differance!
    I have the 10.25 ring gear. Being an Old Timer Ford guy I should have known better to take the old cover with me!
    It looks good with the new gloss black paint and the chrome cover.