Question

The bus (broke-was broken) down?

Answer 1

"The bus had broken down." "The bus was broken down."

Explanation:

Subtle differences. "The bus had broken down" would refer to the bus recently breaking down. "The bus was broken down" may be a general description of the bus (a particularly bad looking bus) rather than the fact that it was not capable of moving. It could also mean the bus had broken down.
"He drove a broken down old bus."