Lunchbox locker.....friction modifier needed?

    I'd like to change the gear oil in my front differential, but am stumped when it comes to friction modifiers. I have the D30 axle with a Richmond Lock-rite "lunchbox" locker and 4.10 gears. I've read the owner manual for the locker, and not one word is mentioned about adding a friction modifier. Yet, I have a nagging feeling that I added a friction modifier last time I changed the gear oil.....but my memory fails me (again). I'm planning to use a 90 weight oil. Can anyone chime in on this?


    Related to this......in the rear I'm running a Ford 8.8 axle with (obviously) 4.10 gears. Same gear oil weight in the rear as in the front? I'd assume so, but I have a long history of making bad assumptions.

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    Chief, DEJA Grammar Police

    Quote from Chief57


    One last thought..... Apparently I've been handling my lunchbox locker gear oil incorrectly all this time. I've been adding friction modifier to the gear oil, but I shouldn't be doing that with this type of locker. So, the oil I added yesterday was without the modifier. Maybe that change in itself will be beneficial.


    ...something about history repeating itself? :)

    Friction Modifier only affects clutch type limited slips. It will not harm or affect other lockers that I am aware of. It prevents the clutch pack from shuttering by increasing/decreasing the friction coefficient of the gear oil .

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    Ok thanks everybody. What we've learned in this thread is....


    - No friction modifier needed for the lunchbox in the front.
    - Friction modifier needed for the 8.8 rear, but there's a Ford-approved synthetic that I will use.
    - I will forget all this and ask these questions again in approximately two years. It's not easy being me. :spinrhead:

    When engaged in conversation with a fool, be sure he is not similarly engaged.
    Chief, DEJA Grammar Police

    Quote from keith_c

    And only if it has the LSD, and only if the clutches aren't already worn out.


    They usually only last 60K or so.


    Keith, my 8.8 does have the limited slip differential. Given that it's from a 1998 (I think) model Explorer, it probably has well over 60K miles on it. So, for the benefit of the learning impaired, do I need the friction modifier? If not, can I just get a 90 weight gear oil and use it for both front and back differentials? Sorry to drag this thread out, but this is good information.

    When engaged in conversation with a fool, be sure he is not similarly engaged.
    Chief, DEJA Grammar Police

    If it chatters add the modifier.


    There are various opinions on the web as to what weight the 8.8 prefers.


    Nothing magical about gear oil. If you feel better running the thicker stuff, do it.


    With 80/90 it will probably outlive us both.


    I wouldn't waste money on synthetic.

    Every official ford book says 140.,there is good reason for the thick stuff because the backlash on ford gears is almost double of a dana axle. It also holds to the gear better as it moves through the diff.

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