In a nutshell, Hydroboost setup is similar to Powerboost in that it uses hydraulics not vacuum to actuate brakes....However, unlike the Powerboost which utilizes an accumulator and electric motor, the Hydroboost simply uses the existing Power Steering Pump to generate pressure. The Hydroboost was used on earlier Hot Air GNs. It gives stronger brakes than vacuum (the general consensus anyway) and much less prone to failure since the power steering pump is always turning when the engine is running (no electric motors to fail or accumulators to leak).