The Stovebolt Site Forums The Shop Area Driveline Transmission casting numbers

As I move toward an open drive line in my 54 with manual trans, I find many transmissions for sale that can be accurately evaluated only by the cast or stamped numbers. I have found the necessary decoder for engine numbers, but similar for transmissions are skewed toward automatics, and a search of this forum wasn't sufficient, and AI isn't as smart as it claims. The unit I am currently looking at has cast numbers GM4, GM H246, and 8889564. I believe it is a 1960s 4 speed, but have no more info than these numbers. Is there a comprehensive list of casting numbers for the several makes of GM transmissions?

Can you provide pictures???

Many casting numbers can be found in the Chevy Master Parts Books, using GM Partswiki searchable database. I just did a quick check using that casting number and came up with no matches unfortunately.

Casting numbers are notoriously known for being difficult to read/easy to misidentify, so picture are a big help getting past that issue. Also of importance is the transmission has many different casting numbers. Main case, tail shaft housing, side cover, etc. The most important one to start with will be the one on the main case.

Please post some pictures,if you can and we offer more help.

As a follow up to above, the transmission should have a "stamped" (not cast) Alpha-Numeric serial number on the main case, often on the tail shaft housing mounting flange or the side cover mounting flange (machined surface). That info can also be decoded to help identify the unit, coinciding with the main case casting date code.

"H246" in general decodes as August 24th 1956 (or 1966 or 1976), as the last digit only indicates the year but not decade built.

That particular unit is no longer available, but having a list of numbers would be handy as I forge ahead. Deve's list of engine casting numbers was spot on and easy to use for my engine.

Hollander goes by casting number rather than part number because salvage dealers went by casting numbers rather than by part number. However casting numbers are not indexed. The casting number you cite does not come up to a Chev or GMC 4 speed in my 1966 edition of my Hollander. A 48-54 SM 420 will hve a casting number of 591907. If it is in a half ton, it will be a torque tube. a 3/4 and 1 ton uses the same case with a half closed drive shaft. a 1 1/2 ton uses the same case but is open drive shaft. A SM 420 with a casting 3837332 would be a 55 and later with an open drive shaft.

Try looking at Novak transmission site it has a description of the casting differences between the years of the sm 420 but not sure on the numbers .if you want a open drive using a sm 420 they were used from around 1948 to 1969 with small differences the older ones will work but you will need the rear bearing cover from a newer one with the yoke for the u joint and seal .The 68/69 ones have a reverse light switch on the top cover.There also may be newer models that were used in military vehicles.

SM465 came out in 1968, replacing the SM420 in most applications. SM420 continued in some military application afterwards.

Shopping for a SM420, I would look for a 7 digit casting code which indicates a later model. You can still get syncro rings for the later models. If it has a backup switch, that's a bonus.

ps. the casting code 8889564 was probably 3889564.