What kind of transmission does a Chevy sm420 have?
What kind of transmission does a Chevy sm420 have? The SM420 is the older heavy duty, granny, 4 speed transmission used in Chevy and GM trucks. The large cast iron case with large bulge on the passenger sidemakes it easy to identify. Which is heavy duty Granny 4 speed transmission? The SM420 is the older heavy duty, granny, 4 speed transmission used in Chevy and GM trucks. The large cast iron case with large bulge on the passenger sidemakes it easy to identify. It is an excellent 4 speed to swap into a Jeep with a Chevy or Buick engine....