[66Submarine]

Is it pulling hard left or right, or just locking up the rear? Either way, it has nothing to do with the lack of a power booster; that would just lessen the pedal effort needed to do so.

The drum size is critical for good braking performance without pulling to one side. When you turn the drum out and increase it's diameter you reduce shoe contact area and make the brakes less effective for that wheel as a result.