Preheat oven to 350 degrees. Spray 3 9-inch cake pans with nonstick baking spray.
In a medium bowl, whisk together the flour, baking soda, cinnamon and salt. Reserve.
In a large bowl, beat together sugar and vanilla until fluffy. Add the eggs, one at a time, beating well after each addition.
Add flour mixture to butter mixture, alternating with buttermilk, beating until just combined after each addition. Then add in the bananas and pineapple and beat until combined.
Equally divide cake batter into prepared pans. Bake for 30 - 35 minutes or until wooden pick inserted in center comes out clean. Cool in pans on wire rack for 10 minutes. Then remove from pans and cool completely on wire racks.