Volvo: brake pump valve, electric vacuum pump, vacuum leak

Question
I have a 2000 Volvo S40 Turbo. After having my brakes serviced (pads and rotors), the brake pedal would go almost to the floor.  I could pump them and the brakes would work, but it continued to worsen to where now I cannot even get the car in gear. I have been told it is the brake pump valve. The part was recalled, but has expired.  I have a little bit of mechanical experience, just not with Volvos. I would like to know the location of the part, and how difficult it would be to change.  Thank you for the help.

Answer
Tamara,
Look under the brake booster and you will find an electric vacuum pump. There will also be vacuum lines coming off the pump. It is in a tight place, so there is some difficulty to the replacement. First though I would make sure that there is not a vacuum leak in the system before replacing the pump.