I have a 98 grand Cherokee limited 5.2 all time 4x4. Between 45 and 55 mph it feels like my right front brake engages all by its lonesome few a few seconds to a few mins and then let's go. It does it all the time. I have replaced the bearing and hub assembly as well as new calipers and brakes... I have no idea what could be causing this problem and I need to fix it ASAP as this is my daily driver. Thanks.

 

Did you also replace the rubber the brake line that runs to the calipers? Lines can collapse internally sometimes and cause the calipers to bind.

 

Is this happening by itself or when you hit the brake? If it's happening by itself, I'd go with Crazy's scenario. the hose is collapsed internally and not bleeding the caliper completely. This causes the pads to ride on the rotor and build heat enough to boil the fluid, thus causing the brake to set. The hoses are easy to replace and I'd suggest you do all three. Make sure you didn't twist the hoses when you replaced the calipers. The hardest part is loosening the steel line flare nut without destroying it.