I'm helping a friend sell his 1984 CJ. All the vin decoders I found say the 5th digit is for trans. His 5th digit is F. I can't find F on the decoders for that year. For 81-86 it shows the 5th digit as being B, A, M, or N. 75-80 has an F for three speed. I'm picking up the Jeep tomorrow to look at it but he says it's a 4 speed. 4 speed would make it M. Here is the vin.