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NP208 - Gear Oil or Tranny Fluid?

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by 1986Blazer, Jul 31, 2001.

  1. 1986Blazer

    1986Blazer 1/2 ton status

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    What would the damage be if thicker gear oil was used in the NP208? I found a GM Tech that said the gear oil may actually help the NP208? Has anyone dealt with this question or actually used gear oil with no damage?

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  2. newyorkin

    newyorkin 1 ton status

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    I never actually saw it happen, but supposedly the sulfur and other additives in Gear oil will damage the aluminum casing of the 208.
    Before I knew that, I put gear oil in a Jeep manual tranny that originally had ATF. It drove on the gear oil fine for a long time, and for all I know still is...

    Ratch
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  3. ftn96

    ftn96 1/2 ton status

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    Ditto, I heard the same thing.

    I pay ya to work it not jerk it![​IMG]
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  4. 1986Blazer

    1986Blazer 1/2 ton status

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    With the organic base of gear oil (just specially refined crude oil) - would not synthetic gear oil be compatible??? I would think the sulfers and other components would not be present in the syn oil....I'm just typing out loud here.

    So I says to him, I said, "get your own monkey."
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  5. newyorkin

    newyorkin 1 ton status

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    I'm not too sure, but I think sulfur, etc, is added to the conventional gear oil for something to do with the gear metal and wear protection, so it may be present in synthetic too. If it's added to do something for the oil, such as keep it consistent, then yeah, it shouldn't be present in synthetic.

    Just curious, why do you want to switch to gear oil? Just wondering.

    Ratch
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  6. jarheadk5

    jarheadk5 1/2 ton status

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    If I recall correctly, the sulfur and phosphorus are in petroleum-based gear oils to improve their stability under the high pressures found in-between gear teeth. Petro-based gear oils rated EP (Extreme Pressure) stink worse than regular gear oil, so that leads me to believe there's more sulfur &amp; phosphorus in the EP vs. the non-EP. I'm not sure if they're present in full-synthetic gear oils; I don't have any experience with them.
    The 208 and most other newer T-cases went to straight ATF because it sucks up less power than gear oil, hence better efficiency. I don't know why straight ATF is bad in early T-cases if it's good in later T-cases (old 205 vs. "newer" 205). Maybe better alloys or different heat treatment of the gears/bearings...

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  7. dyeager535

    dyeager535 1 ton status Premium Member

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    A better question might be "why would you not use what GM recommends"? Not trying to be a smartass, but ATF can typically be purchased for less than gear oil. Leaks faster prolly, but it also gives you better economy.

    Dorian
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