93 International 4700 dt360 hydromax booster - brakes hard to press

I just purchased a 93 International navistar 4700 (dump truck) and the hydromax booster and master cylinder were both leaking so I changed them both. I bleed the master cylinder on all four calipers until no air bubbles and new fluid. The problem that I'm having is I dont have and assist from the hydromax booster, brakes are hard to press and pedal is way up top. Any Info greatly appreciated.