The ABS pump is there to provide boost pressure to aid in stopping. There's a pressure accumulator and a rather complicated assembly of hydraulic pistons called a modulator that act to bring the heavy beasts to a quick stop with very little brake pedal effort. There's a lot of information thoughout this site on repairs that can be made to the system, each component providing it's own unique challenge. Can't say what one item is causing the failure. I suspect it may systemic due to the long term use without the ABS pump providing needed boost pressure. Perhaps you ran it in emergency mode for a little too long. Try starting with a forum search for "brake modulator", and read on from there.