Trying to ID my SM420 transmission so I can buy new parts... the Novak-Guide says that '64-67 transmissions have a 7 digit casting number with aluminum 2nd gear synchro and identical 3rd & 4th synchros
My transmission has a 7 digit casting code, however, the date code ends with a 9 (indicating 1959) The 3rd and 4th synchros appear to be identical, but my 2nd gear synchro cone & teeth appear to be steel rather than aluminum.
So maybe the novak guide is wrong & they actually used 7 digits in 1959? Or maybe I have a '64-67 transmission where they screwed up the date code? Doesn't seem like my 3rd and 4th synchros should be identical if there are steel parts for 2nd gear synchro rather than aluminum?
Ott, they are talking about the friction material (aluminum vs steel) that is housed within the first gear. This is what is used to slow the 2 nd gear syncro ring. I have only ever seen one that was worn enough that warranted replacement out of a dozen or so transmissions that I have worked on this last year. As far as I know the friction material is unavailable by itself necessitating replacing the entire first gear if needed.
Steve
Last edited by sstock; 10/16/201912:28 AM.
1953 Chevrolet 3100 261 cu inch, sm420, 3.55 rear, torque tube still,omaha orange, still 6 volt, RPO green glass, side carrier spare, all done In the DITY Gallery Video of the 261 running
1964 GMC 1000 305 Big Block V6, sm420, the next cab off restoration
Whoa, you work on a lot of transmissions! Thanks for the distinction... mine does shift nicely into 2nd and the friction material (within 1st gear) is bronze.
I'm mainly needing to replace the 3rd gear synchro and am debating to do the bearings while i'm at it. Present bearings 'seem' ok and are labeled 'New Departure' made in USA
Yes excuse my typo, most are bronze. To replace the 3rd synchro you will need to remove the clutch gear and press the rear bearing off the main shaft to get the gear cluster out of the case. The hub will need to be pressed off the main shaft to get to the 3rd synchro. Occasionally they pop up on ebay. There is one in there now https://www.ebay.com/itm/1948-1949-1950-1955-chevrolet-4-spd-truck-1st-gear-countergear-nos-gm-591602/123819292750?hash=item1cd434784e:g:PRwAAOSwV4xcu31W
cheap enough
Last edited by sstock; 10/16/20192:32 AM.
1953 Chevrolet 3100 261 cu inch, sm420, 3.55 rear, torque tube still,omaha orange, still 6 volt, RPO green glass, side carrier spare, all done In the DITY Gallery Video of the 261 running
1964 GMC 1000 305 Big Block V6, sm420, the next cab off restoration
