Your system is probably AIR OVER HYDRAULIC. There should be a bleeder at each brake location. Mine are discs all the way around. You will need to have the system air at operating pressure (over 65 psi) then have someone press and hold the pedal. Crack the bleeder. Close it release pedal (give it time for the air system to retract the master cylinder plunger. Repeat.
97 Beaver Patriot, Cat 3126, Aqua Hot