Clunk noise when using rear brake

[leenaqvi]

I had a friend put new tires on my GZ250. After putting the rear wheel back on the the arm that engages the brake (the brake cam lever) was pointing straight up instead of straight down. He took off just the brake cam lever and rotated it 180 degrees to make it point down. After everything was put back together when I first pressed hard on the rear brake there was a loud clunk and then the brake engaged. Now every once in a while there is a clunk when applying the rear brake. Does anyone have an idea what the problem could be? I am suspecting that the rotating of the brake cam lever might have caused a problem? Unfortunately that friend is no longer around and my mechanical skills are limited.

brake cam lever.jpg