【break down】 —

1. (of machinery) fail to operate:

• The car broke down on the way to the airport, and I had to take a taxi.

2. (of an attack, talks, etc.) fail; come to nothing:

• I expect the negotiations to 【break down】 soon.

3. suffer emotional disorder; lose control of oneself:

• The task before her was so difficult that she almost broke down in performing it.

【break up】 —

1. (of things) separate into smaller pieces or parts:

• In spring the ice on the Great Lakes breaks up.

2. (of a party, meeting, etc.) come to an end:

• The party broke up when the police arrived.

3. (U.S. coll.) convulse with laughter; be greatly amused:

• Peter just broke up when we told him what had happened.

4. (of married people) separate:

• She had heard that John and Lucille had just broken up.