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noisy rebuilt muncie m-20..help!!

Discussion in 'The Hokey Ass Message Board' started by 70chev, Aug 5, 2013.

  1. 70chev
    Joined: Apr 14, 2013
    Posts: 20

    70chev
    Member
    from knox, pa.

    Had my 1970 vintage M-20 Muncie 4 speed rebuilt by a reputable old shop, complete rebuild, all parts except the main shaft [ it was checked and deemed to be OK so we used the orig.] are new old stock Muncie/GM parts other than the bearings..The supplier also has a good rep and is working with us on this but; The transmission whines loudly in 3rd gear when put under any kind of a load...With no load at all, i.e. starting out slowly or on a downhill the transmission makes no noise at all..All other gears are OK, the transmission shifts perfectly...We adjusted the shifter a few times to no avail..Tore the transmission down after about 75 miles and see no problems..The trans shop called the parts supplier and someone there said 'we have this happen once in a while' and supplied a new main cluster gear to replace the other new main cluster gear, no change..There are no grindings or shavings in the transmission oil, I am running 50% 80-90 gearlube and 50% Lucas transmission oil..The transmission shop is standing behind their work but they are stymied...Anyone have any ideas/suggestions? I would really like to drive this car to Joplin pretty soon.....
     
  2. 70chev
    Joined: Apr 14, 2013
    Posts: 20

    70chev
    Member
    from knox, pa.

    Thanks for the info, I don't understand why the gear supply place thought the cluster gear would have anything to do with the problem either, but they overnite shipped us one. The gears were made in the U.S.A. The bearings are Japanese. Thanks again..
     
  3. BOBCRMAN
    Joined: Nov 10, 2005
    Posts: 846

    BOBCRMAN
    Member
    from Holly

    If the wrong synchro slider (1-2) is used on the 3-4 synchro assembly. You will get noise. The outer edge will just barely touch the cluster when in third gear and make much racket.

    Looking at the sliders, the 1-2 slider has a more or less square thick outer shoulder, fork groove around the center and taper to other side. and the 3-4 is tapered from the outside edge to the center more, fork groove, then taper to side.

    Been there!!!!
     
  4. 70chev
    Joined: Apr 14, 2013
    Posts: 20

    70chev
    Member
    from knox, pa.

    Thanks for the comebacks, been without internet service a while...I forwarded the advice to the shop, as stated just now getting back on line [on a motorcycle trip in the west] and have not heard from them..Again, thanks...
     

  5. Skunkman
    Joined: Jun 1, 2021
    Posts: 4

    Skunkman

    Hello from France... I know this is quite an ancient post,but i'd like you to ask how you sorted this out... I have experienced the same situation.
    I have been rebuilding a 65 M20 Muncie ,out of a Corvette.
    Everything is new in the case... (got all the parts from "the gearbox.org")
    And the 3d whines under load ,exactly the same way yours does or does'nt when downhill or slow...
    Pushing the gear lever forward reduces the noise...

    I am puzzled.

    Thanks for your attention.
     

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