One problem related to brake master cylinder has been reported for the 1998 Volvo S70. The most recently reported issues are listed below.
While braking, the vehicle vibrated. Took vehicle to dealership and the mechanic indicated there was a crack in the brake master cylinder. The abs light illuminated, the oxygen sensor was replaced, the vacuum line was replaced, the upper torque arm bushing broke, the door locking system broke, the inside door panel came apart.