One problem related to brake master cylinder has been reported for the 1999 Jeep Grand Cherokee. The most recently reported issues are listed below.
Had occasionally heard a sound outside the vehicle like a hose letting off air . . . Figured it was the compressor. Today, I got in the vehicle and backed out of my garage and heard a steady flow of air that sometimes rose and fell in pitch. I determined that a flexible housing covering the linkage from the brake pedal to the master cylinder vacuum booster had burst open after what appears to be shearing from continual wear on the rubber boot itself. I do not know what this is caused by or how serious it is. I still have brakes, but under what conditions I do not know. The shearing of this rubber by the mechanism itself appears to be something that could be in common with any Grand Cherokee. Please let me know what your find out.