Ford's safety compliance certification label on the driver's side door jab will identify the automatic transmission with a single letter. A metal identification tag can be found on other Ford automatic transmissions.
Decoding the Letter
The letter "V," for example, identifies the transmission as a C3 in the 1983 Ford Ranger trucks equipped with a 3-speed automatic with gear ratios of 2.47, 1.47 and 1.00 (see Reference 2).
The letter also identifies the engine size of a Ford, such as "D" identifying the 5R55E automatic in 1997 to 2009 Fords equipped with 4L engines (see Reference 2).
On C-4, C-5 and C-6 transmissions below the servo cover bolt is a metal identification tag embossed with model prefix and suffix numbers, five-letter transmission model number and build date, according to allfordmustangs.com (see Reference 3).
C-4 vs. C-5
The C-4 and C-5 have physical differences. The C-5 features a different hydraulic system with more valves and a converter relief vale switched from the pump to the assembly reactor support, according to the rangerstation.com (see Reference 2).
The letter "P" in a casting number on the transmission denotes an automatic, while an "R" identifies a manual transmission (see Reference 1).
Identical "P" and "R" letters are found stamped on other Ford parts, making the safety compliance certificate a better method of identification, according to mmerlinn.tripod.com (see Reference 1).