4L60 (700-R4) Automatic Transmission

Transmission identification code can be located in one of two positions: right rear pan to case mounting flange or right side transmission to engine mounting flange. The first digit of the transmission identification code denotes what model year the transmission was built The second and third digits of the transmission identification code denotes transmission model. The fourth, fifth and sixth digits denote the Julian date which tells what day of the gear the transmission was built. It should be noted that the transmission model year starts MID YEAR. This means that the first transmission built in any model year will start with a higher Julian date.

For example; if the first transmission in 1984 was built on August 5, then the Julian date starts at 218 and goes to 365 (which is December 31). The Julian date will then drop to 001 (which is January 1), and then continue to 217 (which is August 4, 1985).