BB vs SB 4-speeds

Discussion in 'U-shift em' started by Greg B, Feb 8, 2006.

  1. David Hemker

    David Hemker Well-Known Member

    71 GS's are the hardest to verify due to no special vin code for engine size.

    On Buick 4 speeds, there is no difference between a bb & sb 4 speed muncie.

    There is:
    the M-20 wide ratio with 2.52 1st gear,
    the M-21 close ratio with 2.22 1st gear,
    the M-22 heavy duty with 2.22 1st gear AKA rock crusher. These had straighter cut gears (noisy) & different steel alloys for strength.

    Buick used exclusively the M-21.

    70 & older Muncies were the 10 spline input.
    In 71 there was a design change on the Muncies.
    71 & newer Muncies were the 27 spline input.
    All M-22's were 27 spline input regardless of year.

    If there is a 10 spline Muncie in a 71 & newer car it was swapped in.

    For more info, parts etc go to www.4speeds.com.
     
  2. CJay

    CJay Supercar owner Staff Member

    They used M-20s as well. It depended on the final drive ratio.

    What information are you baseing that from?
     
  3. David Hemker

    David Hemker Well-Known Member

    Chassis manual and experience.
     
  4. CJay

    CJay Supercar owner Staff Member

    The only reason I question you is that I owned a 22,000 mile original 73 GS 350 that had a 10 spline M-20. I would just need some additional confirmation on those statements. maybe Duane "the thread ender" Heckman can chime in on this one
     
  5. David Hemker

    David Hemker Well-Known Member

    All the information I have come across over the past 28 years from manuals, articles, people with more 4 speed experience, parts suppliers etc have verified my earlier post.

    I do know from past experience that for street manners even my 455 likes the wide ratio M-20. I have driven a few 350's as well. I can see where the 73 with lower compression and more weight would greatly benefit from the
    M-20. My guess is the original owner had one sitting around or found one had it changed over. But stranger things have happened.
     
  6. ts-gs

    ts-gs 68 GS400 Convertible

    If the M-20 was original to the car, shouldn't there be a matching VIN stamped in it where the tail meets the housing?
     
  7. Greg B

    Greg B Well-Known Member

    I didn't look for a matching tranny yet but was hoping that there was a unique 4 spd like the BB TH400 for the Stage 1 or at least the big block cars.
    ________
    Ford Transit
     
    Last edited: Mar 22, 2011
  8. David Hemker

    David Hemker Well-Known Member

    The build date and VIN should be stamped on the passenger side of the main case towards the top just in front of where the center support and tail shaft housing bolt on. I have seen the last 6 digits of the VIN and I have seen the last 8 digits of the VIN stamped here.
     
  9. Qship

    Qship Member

    David my original 1970 GS 350 had 3.23 gears and was original with a M20 and yes I checked the serial number and it matched the VIN. So Buicks did use the M20.
     
  10. IDOXLR8

    IDOXLR8 Senior Member

    4-Speed For Me

    1972 was easy, I think power disc brakes and the 3:42 posi was a standard issue in that year, AL.
     
  11. David Hemker

    David Hemker Well-Known Member

    That's interesting. All information in the Buick manuals I have list the M-21 only and make no mention of the M-21. I had a 70 350 car with 3.23 gears that had the m-21.
     
  12. CJay

    CJay Supercar owner Staff Member

    The type of manual trans GM used was dictated by the rear axle ratio. Muncie M-21 & M-22 trannies (and their 2.20:1 1st gear) work best with a numerically high rear axle ratio (3.70 and up). Mating an M-21 with highway gears causes excessive wear on clutches and weak acceleration. Which is why GM used the M-20 in these situations
     
  13. 70GREENROCKETS

    70GREENROCKETS Well-Known Member

    M 20 Trans In 70 Stage 1

    Just fyi my 70 stage 1 ac 3.42 rear built 09\03\69. On the body shop inspection paper i found in the dash it has M20 typed in @@@@@@s!! so at least its on the FLINT paperwork. Gregg
     
  14. Marco

    Marco Well-Known Member

    Hi Gregg -

    M20 is the Buick UPC code for a manual 4-speed transmission, just as M40 is the UPC code for the TH400. It does not represent a Muncie 'M20' transmission. If you have your original trans, look at the verticle stamping on the passenger side and you'll see the stamping ends in a 'B', which represents an M21.

    Notice how Buick has only one UPC code for a 4-speed transmission? :Brow:

    UPC codes can be found on the 1970 new car order form found HERE.

    :beer

    :3gears:
     

Share This Page