don:
m20 gear ratios are as follows
1st: 2.52:1
2nd : 1.88:1
3rd :1.46:1
4th: direct
reverse:2.59:1
Both the m20 and m21 carry the same casting numbers.
The 1966-70 m20 (wide ratio) has 10 teeth on the input splines and 2 grooves.
The 1966-70 m21 (close ratio) has 10 teeth on the input spline and 1 groove.
the 1966-70 m20 and m21 both have 27 teeth on the out put spline
1966-70 m20 and m21 countershaft pin diameter is 1 inch
there are 21 maindrive teeth on a 1966-70 m20
there are 26 maindrive teeth on a 1966-70 m21
there are 25 teeth on a 1966-70 m20 cluster gear
there are 27 teeth on a 1966-70 m21 cluster gear
So as we can see the output splines have different amount of grooves,
different amount of teeth on the maindrive and different amount of teeth on
the cluster gear.
I hope this will help you out.
Larry
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