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POSI vs Locker vs Limited slip

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by GMC4by4, Jun 10, 2000.

  1. GMC4by4

    GMC4by4 Registered Member

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    I replaced my rear outer wheel bearings today. Now I'm not sure which rear lube to use. The ID # on my rear indicates that I have a POSI rear. But I opened it up and I have a bunch of small springs and gadgets with a big square piece in the middle that makes removing the c-clips difficult. That tells me that I have a locker not POSI, right? But then I hear people using the words POSI and Limited Slip interchangeably. My synthetic oil jug says that it can be used in Limited Slip rears but it doesn't mention POSI. So, my question is, do I need to use POSI gear oil or can I just use synthetic or regular? Thanks.

    -Rick
     
  2. keith

    keith 1/2 ton status

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    My 12 bolt rear had a Gov-lock which was news to me. I replaced it with a lock-rite. but before I just used regular diff libe.
     
  3. BB454

    BB454 1/2 ton status

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    Anything that has actual CLUTCH plates on the inside would need the specific LS/POSI-lube. Since gears are not friction bound they only need regular lube. Guv-Loc uses clutch plates and as such uses the LS-lube. Hope this helps.

    BB454
    IF IT DOES NOT HAVE 8 PISTONS - IT'S BROKEN !
     
  4. Thumper

    Thumper 1/2 ton status

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    Well, the way It was told to me is like this:
    Locker: positive lock, no slip, no release. Like an ARB, locked full time unless its shut off or released.
    Posi: A unit that locks when the wheels are travelling the same speed in a straight line, its locked all the time unless a differential is created in a turn (on pavement or hard surface) then it will slip or ratchet allowing the outer tire to turn at a different speed than the inner. like a Detroit Locker
    Limited Slip: a unit that is open until a different torque is sensed between the wheels (eg. one wheel spins), then governors or other devices tighten to engage the clutches, limiting the wheelspin and transfer some torque to the other side that has traction. Like a Gov-Lock
    I had a Gov-Lock limited slip in my Jimmy for a lot of years, GM recommended I use 80w90 oil and a posi additive.
    I now have a TruTrac posi in the rear and the 4x4 shop recommends that I use a posi additive as well.
    As for the locker lockers, Im not sure.
    Hope this helps

    Mike


    <font color=blue>Thumper
    85 Fullsize Jimmy
    [​IMG]
    <font color=red>Lets Go Wheelin! </font color=red>
     
  5. bigjbear

    bigjbear 1 ton status Staff Member Moderator

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    Neither Tru-tracs nor Detroit Lockers need a L/S additive, as they have no clutches. Jim.

    BigJBear '80 GMC
     
  6. 6.2Blazer

    6.2Blazer 1/2 ton status

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    Posi and limited slip are basically the same thing. "Limited slip" is the general term while the term "posi" originally came about because GM started calling the factory limited slip option "positive traction" or "posi traction", and then just people began referring to it as just "posi" and has kind of just stuck as a nickname or slang term for a limited slip (kind of like when people say let's go Jeepin', or call an old Landcruiser or Bronco a Jeep).
    Of course, there are at least a dozen different types of limited slip differentials on the market and while the designs may be vastly different, they are all designed to serve the same purpose at the end.
    Also, Detroit Tru-Tracs and most lockers (Detroits, ARBs, lock-rites, and no a GM Gov-Lok is not a true "locker") do not require a limited slip fluid additive. The additive actually modifies the friction characteristics of the gear lube and is supposed to help the limited slip clutches operate smoothly.....so as already stated....no clutches = no additive needed.
     
  7. Thumper

    Thumper 1/2 ton status

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    Ummm an ARB isnt a true locker?? What is it that fits your description of a 'true' locker? I was under the impression that an ARB when locked, wont differentiate at all... that says 'locker' to me.

    Mike




    <font color=blue>Thumper
    85 Fullsize Jimmy
    [​IMG]
    <font color=red>Lets Go Wheelin! </font color=red>
     
  8. 6.2Blazer

    6.2Blazer 1/2 ton status

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    Yes, an ARB is a true locker and I never said it wasn't. The statement mentioned that Detroits, ARB's, and lock-rites were lockers, but that a "GM Gov-Lok is not a true locker".
    Sorry for the confusion.
     

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