Muncie 4-Speed Identification Guide
2021-2-9 · The progression of the 10-spline input identification groove system. From left to right, early M20, M21, later M20, and M22. You really cannot get the early M20 and M22 mixed up because the early M20 came with a 7/8-inch …Muncie 4 speed....M21, M22, Rock Crusher? - The H.A.M.B. · TonyMemberfrom Rochester NY. USA. ""You can outfit an M20 or M21 with Rock Crusher type gears, OR actually make a 3 speed O/D out of a 4 speed case. Forth being the overdrive obviously.. Actually the 3rd gear station becomes the OD and the 4th gear station becomes 3rd,so the shift pattern is a little weird,1-2-4-3.