How do you read the code numbers of my Muncie 4speed? The numbers are P1228. I know the P is for Muncie but the Muncies after October 21, 1968 used a different number and letter code than before this date. Mine appears to be of the before 68 dated code.

What is your cast number of your Muncie case?

can you tell me what I have ? The #'s I got off the tranny are as follows p7c207 , 3885010 , 7a160048 thanks scott

My cast numbers are 3857584

My cast numbers are 3857584

This is your tail extension cast number.

Jody, Sorry about that. The casting number above the patent number is very faint compared to most Muncies I have seen. It looks like #3985010. It's not high profile lettering like the others that I have seen. Also, do the numbers that I originally stated in my first post (P1228) reveal the first gear ratio like the later Muncies? By the way thanks for replying to my questions.

Jody, Sorry about that. The casting number above the patent number is very faint compared to most Muncies I have seen. It looks like #3985010. It's not high profile lettering like the others that I have seen. Also, do the numbers that I originally stated in my first post (P1228) reveal the first gear ratio like the later Muncies? By the way thanks for replying to my questions.

Your Muncie is a December 28, 1966. Your "P" stamping on a '66 does not distinguish if it is an M20, M21, or M22. Do you have any ID groves on the maindrive gear clutch splines?

Jody, Thanks once again. I can't remember the grooves on the maindrive splines when I installed it but was told by the previous owner that it was an M20..

Jody, Thanks once again. I can't remember the grooves on the maindrive splines when I installed it but was told by the previous owner that it was an M20..

If you have an even RPM drop from 1st thru 4th, you may have an M21 or M22. An M20 will have a much more noticable RPM drop from 3rd to 4th.