Transmission Code Guide
As explained in the Part Numbering Guide, the Base of a part number (disregarding any Prefix letters it might have), begins with a 2- or 3-digit number that signifies the transmission unit that the particular part fits. This is called the Transmission Code.
For example, rebuilder kits and replacement parts for a GM 4L60E will begin with a "74", while part numbers for a CD4E will begin with a "96".
To view the complete Transmission Code Guide, click the download above.