I have made the soda cake twice now. Once I used a can of ginger ale and a Betty Crocker spice cake. I made cupcake with it. Cupcakes were delicious, but they were very crumbly you could hardly get a bite of one because it went into smaller crumbles!
I was determined to try a different soda cake to see if it was maybe the cupcakes that were an issue.
The second cake I made, and it was a cake - Betty Crocker Devil's Food cake with a can of Diet Coke. The cake stuck to the pan in 2 spots, and i had greased to ensure it wouldn't. Once cake was cooled and iced - it crumbles like crazy upon icing. When I cut a slice it crumbles into pieces. The cake was delicious but it broke down into smaller and smaller crumbles so it was a mess to eat.
I have decided to try a different substitution going forward.

Sorry the cake didn't work for you. Others have mentioned that it can be "delicate" and works best as cupcakes.

I hope you try some of the other recipes her like:
Wacky Cake - http://www.kidswithfoodallergies.org/page/recipe-page.aspx?recid=45&name=Kathy%20P%27s%20Wacky%20Cake
Starlight Cake - http://www.kidswithfoodallergies.org/page/recipe-page.aspx?recid=1556&name=Starlight%20Cake