Brake Lock up

[magnumpi]

My 2000 LC4 sat for a year while I vacationed in the desert. After rebuilding the carberator I got it running. During my first ride (about 5 miles) the rear brakes locked up. I could not move the wheel until I removed the line to the rear hub. I assume that there must be a problem with the master cylinder. Does anyone have any advise on what could be wrong and possible fixes? Can this type of repair be done without special tools?

Thanks