What type of oil for Muncie?

Discussion in 'Transmission & Driveline Topics' started by YoungCamaro, Sep 20, 2009.

  1. YoungCamaro

    YoungCamaro Veteran Member

    Mar 20, 2009
    Just bought an m20 wide ratio muncie. I'm going to be installing it tomorrow and i'm wondering what type of gear oil and how much I need to put in it?
    The chilton's manual I have said 3 pints and the guy I bought it from said 2 pints.
    I put 2 pints in tonight and its right below the bottom of the drain plug, should I add more?

    Also I've read a lot about gl-5 oils ruining the brass synchros, so what weight should I use?

    Please comment if you have experience with muncie 4 speeds. Thanks
  2. warped

    warped Veteran Member Lifetime Gold Member

    Filling the case to the bottom of the fill hole is the proper way. As for the GL5, it is not a weight, but a designator for a certain level of additives. In general, you want to stay with a GL4 rated gear lube, but recently there was a post that certain manufacturers have now offered a GL5 rated lube that will protect the brass synchros. Once Gary gets up and posts, I'm sure he will be more informative. Good luck.
  3. Gary S

    Gary S Administrator Lifetime Gold Member

    Apr 14, 1999
    Bismarck, North Dakota
    You want an 80-w90 or 75-w90 oil. It needs to be a GL4 rated oil, not GL5 rated. We had a post here recently about some of the synthetics being rated for both GL5 and safe for brass syncronizers, but I can't find that post.
  4. YoungCamaro

    YoungCamaro Veteran Member

    Mar 20, 2009
    Thank you for the responses I'm going to look for some gl4 80-w90 at the local auto parts store this afternoon and see if they have any. Thanks again
  5. Dave Nelson

    Dave Nelson Veteran Member Gold Member

    Dec 19, 2003
    Vineland N.J USA
    Your GM dealer has GL-4 part #89021672
  6. YoungCamaro

    YoungCamaro Veteran Member

    Mar 20, 2009
  7. Caperns

    Caperns New Member

    Oct 21, 2008
    Cape Breton
    Most manufacturers of manual transmissions and
    transaxles recommend an 80W or 90W GL-4 lubricant.
    GL-5 gears oils which are required in hypoid differentials
    are not used in most synchromesh transmissions
    because the chemicals used to provide the extreme
    pressure protection can be corrosive to synchronizers,
    which are commonly made of brass or bronze. Typically,
    the use of a GL-5 lubricant in a synchromesh
    transmission will shorten the synchronizer life by one
    half. The extreme pressure requirements of spur gears
    and helical gears found in transmissions are not nearly
    as great as found in rear-wheel drive differentials. A
    GL-4 lubricant provides adequate protection for most
    manual transmissions, unless a unique design
    consideration requires the extra protection of a GL-5.
  8. YoungCamaro

    YoungCamaro Veteran Member

    Mar 20, 2009
    thank you also I will drain the gl5 out and replace with some gl4
  9. jb71camaro

    jb71camaro New Member

    Jul 10, 2009
    Battle Creek, MI
    Good to know, I'm getting ready to fill my M-22. Would suck to use the wrong stuff and have to rebuild again.
  10. cubfan226

    cubfan226 Veteran Member

    Feb 7, 2006
    Arlington, TX
    A while back I drained my non-limited slip differential with 3.08 gears and was directed toward some Valvoline 80w-90 GL5 gear oil. I refilled the diff, but have run less than 100 miles on this gear oil. Is the GL5 ok for this diff, or can the diff be damaged by the GL5? I don't know what a hypoid diff is, but I expect my diff is the original (1970). Thanks.

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