Hydro-Boost
A brake booster system that uses pressurized power steering fluid instead of engine vacuum to multiply braking force.
A Hydro-Boost (or hydraulic power brake booster) is a brake booster system that utilizes pressurized fluid from the power steering pump to multiply the driver's braking force. This is in contrast to traditional vacuum brake boosters, which rely on engine vacuum. Hydro-Boost systems are commonly used on diesel engine vehicles (which do not produce natural manifold vacuum) and heavy-duty trucks with high GVWR ratings.
Because power steering pumps operate at extremely high pressures (often over 1,000 PSI), Hydro-Boost systems provide significantly more braking assistance than vacuum boosters. This results in a firm, highly responsive brake pedal and superior stopping power for towing. The system includes a backup nitrogen-charged accumulator to provide power assist for a few stops if the power steering belt breaks or the engine dies.
Symptoms of a failing Hydro-Boost system include a hard brake pedal, power steering fluid leaking from the booster housing (often dripping onto the driver's footwell carpet), a soft pedal that drops to the floor (failed accumulator), and groaning noises when braking. Diagnostics involve checking power steering pressure and inspect the booster seals. If the booster is leaking hydraulic fluid, it must be replaced.