By the time I was ready to go to work yesterday, the rain had stopped.

By the time I was ready to go to work yesterday, the rain had stopped. And no, they aren't simultaneous. First the rain stopped, then you were ready for work.

"Was ready" and "stopped". Its past tense because you are talking about an event from yesterday. I'm not sure what you mean by simultaneous actions.

There can be two possible cases: ( If you don't use "Stop" and instead use the process that is continuous) But -ing for of stop is not possible here. By the time I got ready to go to work yesterday, the rain stopped. So both are simultaneous process This Link may help you with this: http://www.grammar-quizzes.com/8-6.html