TH350 to M20 conversion

Discussion in 'Transmission & Driveline Topics' started by gorilla, Feb 18, 2018.

  1. gorilla

    gorilla Veteran Member

    101
    11
    Feb 11, 2012
    west monroe, Louisiana
    Just wondering if the same drive shaft from the Turbo 350 trans will work with the M20 set up.
     
  2. 70lt1z28

    70lt1z28 Veteran Member Gold Member

    2,253
    320
    Oct 3, 1999
    Beavercreek, Ohio, USA
    Depends on what year. In 70-earlier the Muncies had the same output shaft as the 350 turbo. 71-later Muncies moved to the 400 turbo output shaft size. Length may also be a bit different.
     
  3. gorilla

    gorilla Veteran Member

    101
    11
    Feb 11, 2012
    west monroe, Louisiana
    Thank you for this information. I will look at the splines and all that and make an determination.
     
  4. badazz81z28

    badazz81z28 Veteran Member

    14,653
    161
    May 4, 2001
    Las Vegas, NV
    You don’t even have to count the splines, the Th400 yoke is noticeably larger in diameter.
     
  5. Cardinal

    Cardinal Veteran Member Lifetime Gold Member

    8,245
    13
    Jun 22, 2003
    Endicott, NY
    M20 & M21 use the "smaller" Powerglide/T350/TH200/700R4 yoke. M22 uses the larger TH400 yoke.
     
  6. BigBlock73

    BigBlock73 Veteran Member Lifetime Gold Member

    1,948
    31
    Jul 10, 2002
    Accord,New York
    70-74 M22 had the large output shaft
    71-74 M20 and M21 had the large output
    Large output is the same as the Th400
    These had the 26 spline input as well
     
  7. 70lt1z28

    70lt1z28 Veteran Member Gold Member

    2,253
    320
    Oct 3, 1999
    Beavercreek, Ohio, USA
    Not so sure.

    I believe that in 70 ONLY the LS-6 Chevelle M22 had the large output shaft. All other 70 M22's had the small output shaft.

    Can somebody confirm? Did 70 Z28's or L78' (the only two Camaro's you could get an M22 with) have the large or small output shaft? This also goes for the input shaft. I believe that the fine spline input shaft was only on the LS-6 Chevelles in 70. In 71, it was across the board on all Muncie 4 speeds. Basically, the LS-6 got the beefed up M22 a year before the others.

    Maybe I am confusing the input shaft changes with the output shaft.
     
  8. ErikNORCAL

    ErikNORCAL Veteran Member

    1,023
    4
    Aug 6, 2003
    now in VA
    gorilla do you have the M20 already, what is the spline count on the front and rear?
    If not, these things are old so verify what you are buying.

    Reason I say this is - have a '68 M22 sitting on the shelf. Everything is date code correct, It has a T350 output but I did research at one point and discovered it isn't too much trouble to change over to T400 output. Economical? Probably not.
     
  9. BigBlock73

    BigBlock73 Veteran Member Lifetime Gold Member

    1,948
    31
    Jul 10, 2002
    Accord,New York
    You are correct on the LS6 Chevelle being the only one to get the fine spline and large output shaft in 70

    To go from TH350 to TH400 output, a bunch of stuff would need to be changed, as well as a complete disassembly.
    Main shaft,tail housing,reverse gear, come to mind.
    It would be easier and less expensive to change the slip yoke on the driveshaft
     
  10. garyandcindy

    garyandcindy Veteran Member

    1,600
    6
    Oct 20, 2004
    cumming,ga-usa
    I changed from 350 to m21 and the drive shaft fit right in. No cutting or joint changes were needed.
     

Share This Page