TRANSMISSION IDENTIFICATION

The transmission identification code will differ depending the type of transmission - Manual, Powerglide, Turbo Hydra-Matic 350, or Turbo Hydra-Matic 400. 

The manual and Powerglide will have a production code consisting of a prefix letter designating the assembly plant, a production date (year/month letter/day number) and a shift code for day or night shift if the assembly plant was using two shifts. 

The Turbo Hydra-Matic 400 used a different date coding format. This production code consists of a two-digit model year (69) followed by an engine/model code letter and a three-digit production date. The three-digit production date begins with the first day of January, 1968. For example, a production date of 299 would be October 25, 1968 or, the 299th day of the 1968 calendar year. (1968 was a leap year, 366 days). January 1 of 1969 would be 367. A Julian date calendar can be found here to assist you. Remember, a production date of 001 to 366 is calendar year 1968 and 367 or higher is calendar year 1969. If the production date is over 366, subtract 366 and find the corresponding Julian date for 1969. It's not known when the last TH400 was installed in a 1969 Chevelle, but assuming July 31 the last model build day, a date of 578 should be the largest date. July 31, 1969 (578) is the 212th day of 1969.  Subtracting 366 from 578 gives you 212 - July 31, 1969.