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 Powerglide and Turbo Hydra-Matic 350 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 (70) 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 1969. For example, a production date of 298 would be October 25, 1969 or, the 298th day of the 1969 calendar year. January 1 of 1970 would be 366. A Julian date calendar can be found here to assist you. Remember, a production date of 001 to 365 is calendar year 1969 and 366 or higher is calendar year 1970. If the production date is over 365, subtract 365 and find the corresponding Julian date for 1970. It's not known when the last TH400 was installed in a 1970 Chevelle, but assuming July 31 the last model build day, a date of 577 should be the largest date. July 31, 1970 (577) is the 212th day of 1970.  Subtracting 365 from 577 gives you 212 - July 31, 1970.

A typical Muncie will break down as follows: P0A01A breaks down to P (Muncie), 0 (1970 model year), A (January), 01 (day), A (M20) . Any Muncie build in calendar year 1969 for an August through December built 1970 model year would be dated with M, P, R, S or T (Aug., Sep., Oct., Nov., Dec.) such as P0R25A meaning the transmission was coded for a 1970 model year Chevelle on October 25, (calendar year) 1969. The letter suffix code identifies the M20, M21, and M22; "A" for the M20, "B" for the M21, or "C" for the M22. Arlington tends to code their 4-speed Muncies a bit different. They may or may not have the letter suffix code "A,", "B,", or "C" or they may have the suffix letter code in addition to the 2-letter broadcast code such as "WO" for an M22, "WL" for an M21, or "WB" for an M20.

Manual, Powerglide, Turbo Hydramatic 350 Transmission Designations
3-speed 4-speed Powerglide Turbo Hydramatic 350
K - McKinnon Industries
S - Muncie
P - Muncie (H.D. aluminum case)
R - Muncie (L.D. aluminum case)
C - Cleveland
E - McKinnon Industries
B - Cleveland
Y - Toledo
Year - 0      
Calendar Month
M - August P - September R - October  
S - November T - December A - January  
B - February C - March D - April  
E - May H - June K - July  
       
Day Number
1...31
 
Powerglide 2-speed and Turbo Hydra-Matic 3-speed Automatic Transmission
B - Cleveland (TH350)
C - Cleveland (PG)
Y - Toledo (TH350)
Variations have been found for Powerglide and TH350 transmission designations. Normal code would be the plant letter, model year, month/day such as B0C14 for Cleveland (B), 1970 (0) March 14 (C14).

A Turbo Hydra-Matic 350 would be coded like Y0E01 for Toledo (Y), 1970 (0), May 1 (E01) with the possibility of D or N for day or night shift.

Turbo Hydra-Matic 400 Transmission Designations
*A sample TH400 code would be 70CF379 where CF indicates a Chevelle 396 engine, CS (454/360) and CY (454/450) indicates a H.D.TH400 and 379 indicates January 14, 1970. Since the three digit suffix is greater than 365, the date must be in calendar year 1970. Subtracting 365 from the 379 number gives a result of 14 indicating the 14th of January. Many times the P-O-P may just code the single letter "F", "S", etc. instead of "CF" or "CS".

A typical Muncie will break down as follows: P0A01A breaks down to P (Muncie), 0 (1970 model year), A (January), 01 (day), A (M20) . Any Muncie build in calendar year 1969 for an August through December built 1970 model year would be dated with M, P, R, S or T (Aug., Sep., Oct., Nov., Dec.) such as P0R25A meaning the transmission was coded for a 1970 model year Chevelle on October 25, (calendar year) 1969. The letter suffix code identifies the M20, M21, and M22; "A" for the M20, "B" for the M21, or "C" for the M22. Arlington tends to code their 4-speed Muncies a bit different. They may or may not have the letter suffix code "A,", "B,", or "C" or they may have the suffix letter code in addition to the 2-letter broadcast code such as "WO" for an M22, "WL" for an M21, or "WB" for an M20.