What transmission fluid do I use?

Discussion in 'Transmissions' started by el40, Oct 1, 2020.

  1. el40

    el40 Newbie

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    I had a nv3500 transmission of a 1998 gmc k1500 5.7 rebuilt and the shop told me to use 10w40 synthetic oil
    But in the manual
    It says to use synchromesh fluid

    what should I go with
     
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  2. 2001ZR2

    2001ZR2 OBS Enthusiast

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    I would use the Synchromesh but really don't understand the 10w40 in the transmission.
     
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  3. Nad_Yvalhosert

    Nad_Yvalhosert OBS Enthusiast

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    If Synchromesh is recomended, Synchromesh is what you should use. It's similar to 5w30 in viscosity, but with different additives. 10w40 doesnt have the additive package so dont use it.
    Go with GM's advice, not "some shop".
     
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  4. F4U-1A

    F4U-1A I'm Awesome

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    Use only the dealership AC Delco Synchromesh. It is designed for their manual. Leaks may develop in the rear seal, if you don't.
     
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  5. 351FUN

    351FUN OBS Enthusiast

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    Personally, I'd trust GM over a random shop.
     
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  6. Pinger

    Pinger I'm Awesome

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    If the oil you guys have access to is GL rated... then GL5 is for diffs etc, GL4 is for gearboxes.
    GL5 has anti-wear additives that will attack yellow metal synchromesh parts. It can only ever be used in manual box if the box has steel synchro rings.
     
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  7. Trenton

    Trenton Just a Texan transplanted in the Rockies

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    If you go the Amsoil website, they give recommend a fluid called "Manual Synchromesh Transmission Fluid, 5w-30" for the NV3500. So yeah use Synchromesh fluid like stated above.
     
  8. Postmech

    Postmech Newbie

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    Use synchromesh fluid. GM has spent millions on specs for their stuff, it works. The TKO500 in my Camaro even uses the stuff.
     
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  9. 1989GMCSIERRA

    1989GMCSIERRA I'm Awesome

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    some transmissions use actual gear oil

    most newer transmissions use a ATF type fluid. My ZF6 uses Mercon V
     

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