One problem related to brake master cylinder has been reported for the 2008 Hyundai Sonata. The most recently reported issues are listed below. Please also check out the statistics and reliability analysis of the 2008 Hyundai Sonata based on all problems reported for the 2008 Sonata.
As others have reported, the brake lines on my 2008 Sonata rusted through causing brake failure while driving on the highway. Repair costs near $600. Service manager states that "every one of these cars will be in for the same problem" due to the design. The two brake lines and two fuel lines which run from front to rear on the vehicle (under the driver's seat) are held in place with clips and then the entire length is covered with a rectangular plastic cover (or raceway). While this might work well in other climates, here in the northeast "salt belt", this cover traps the road salt which collects at the clips and rots through the steel brake lines. Fuel lines are not steel and are not affected. At the very least, Hyundai should require customers to bring the car in for service to have the cover removed and discarded, and the lines washed off and inspected. If corrosion is present, they should repair the damage. Due to the way the lines are routed, the position of the master cylinder and other components, the repair is costly - but is all labor. It is about $50 in parts and $500 in labor.