'69 Z28 Transmission | Team Camaro Tech
1,663 Posts. #2 · Aug 27, 2001. The M-21 is the close ratio 4-speed. It was used on high performance models with numerically high rear end ratios. The M-22 was the "rock crusher". It had the same gear ratios as the M-21. The VIN is stamped on the tranny. The location may have varied.