nissan brake problem

[lazarp]

Hi everyone!
When I use brakes the rear right wheel doesn’t stop. The master cylinder of my car (Nissan Bluebird 1990) Is a bit strange. Alongside the main cylinder there is an other a bit narrower one, and it’s purpose I still don’t know. Some colleagues suppose it is for stopping the brake liquid in relevant circuit if there is a leakage in this circuit.(By means of moving ball inside the second cylinder due to the pressure difference). Now there is no leakage in brake system. There is no other reason than the pressure given from the master cylinder because the manual brake is working properly.
If somebody knows for sure the purpose of the second cylinder and how can I move the ball to it’s original position, please to tell me. Is it possible just to make some bleeding of brake liquid from the left wheel and thus to move the ball in the opposite direction?
Thanks
Lazar