A hydroboost brake assist uses hydraulic pressure supplied by a power steering pump to multiply brake apply force. Hydroboost is indeed a viable alternative to vacuum brake boosters. The right hydroboost unit can be easier to package than a vacuum brake booster while offering far more brake apply force than vacuum. The operation is actually quite simple, but the overall system components and plumbing can seem confusing, at first. Let's take a look at how a hydro-boost assist actuator works and how to ensure proper operation through proper parts selection and plumbing.

Hydroboost Operation Explained

A hydroboost unit consists of a piston that is moved through it's range by pressurized hydraulic fluid. A n input rod at the back of the hydroboost unit is connected to your vehicle's brake pedal. This input rod actuates valves within the hydroboost unit which flow metered fluid into a boost chamber. The pressure in the chamber then moves the power piston with multiplied force. The power piston is connected to an output rod which, in turn, moves the master cylinder rod. With hydroboost, the amount of force required to press on the brake pedal is greatly reduced.
Aside from its basic hydraulic function, a hydroboost unit also has an accumulator component that maintains a pressure reserve.
That's pretty much it. Hydroboost relies on a power steering pump to supply pressurized fluid. Your steering gear, hydro-boost and power steering pump need to work together. Proper plumbing between these components is very important. It's best to work with trusted vendors who can supply parts that are calibrated for your application.

Should You Use Hydroboost In a Performance Car?

Hydroboost was introduced in the 1970s by Bendix for medium-duty trucks used for towing and that experience varying payloads. Dump trucks and dually pickups are great examples. More recently, some large SUVs and pickup trucks feature hydroboost for similar reasons.
What about performance vehicles, though? Hydroboost brakes have found its way onto performance vehicles where the goal is less weight -- not more. Traditional vacuum boosters work just fine on a 3400lb vehicle. Hydroboost may be a viable option for supercharged applications where low engine vacuum is a factor. Limited firewall clearance is a another consideration. If you have large, heavy wheels and tires like on a rock crawler, the extra brake apply force can be useful. Lastly, there is a segment of pro-touring cars running track days with giant 6 piston brake calipers and supercharged engines.

How To Plumb Hydroboost Brakes

Hydroboost brakes may seem complicated. In reality, there are two main rules to hydroboost installation: Rule #1: Danger High Pressure! Extreme care should be taken while plumbing and testing. High pressure AQP hose is mandatory for both your your hydroboost and power steering lines. Some choose to run hard lines, but adequate hose diameter is required to ensure proper fluid flow.
Rule #2: Run completely separate return lines for hydroboost and power steering As shown in the diagram above, you will need a power steering reservoir with two return ports. We do not recommend connecting the two return lines together with a "Tee" fitting. Backfeeding may result. You don't want hydraulic pressure pushing back against the piston in the hydroboost unit.
To understand the diagram above, start at the reservoir. The fitting at the bottom is connected to the feed line (blue hose) which sends fluid to the power steering pump. The red line from the power steering pump feeds pressurized fluid (red hose) to the hydroboost unit. The hydroboost unit uses some of the fluid and passes the rest of the pressurized volume on to the steering gear or rack (red hose). Finally, the steering gear and hydroboost both return fluid to the reservoir separately (green hoses)

Hydroboost Brakes for Hot Rods

When shopping for a hydroboost brake assist system, consider the power steering side of the equation as well as the braking side of the equation. For braking, we found Hydratech Braking Systems in Lebanon, TN on pro-touring.com. As a small company that sells direct, Hydratech can custom-tailor a hydroboost unit that is compatible with your firewall and brake pedal. They offer a master cylinder option that helps you dial the system in to your car's brake calipers and other specs. If you prefer a shop out west, check out Sweeting Performance.
Avoid "one-size-fits-all" hydroboost systems, as you may end up with overboosted or underboosted brake pressure. Overboosted brakes can feel like an on/off switch with poor modulation.

Hydroboost Aluminum Power Steering Reservoir

For the power steering side of the equation, Concept One offers hydroboost-compatible power steering reservoirs with two return ports and a single feed port. The units are 100% billet aluminum and can be remote mounted anywhere. Carved from a solid chunk of aluminum, Concept One's aluminum power steering reservoir is exceptionally strong. A fine thread cap features an o-ring seal. Special internal baffling "calms" returning fluid to reduce fluid aeration. Many phantom hydroboost issues can be traced back to a single return reservoir with no internal baffling.

 

Hydroboost Hose Kit

The last piece of the puzzle is your hose kit. There are A LOT of hose kits on the market, but they are not the same. It is critical to buy a hose kit that is compatible with all of the components in the fluid chain including the reservoir, hydroboost unit, steering box or steering rack and steering pump. Concept One Hydroboost Hose Kits factors in all of these components and has kits with the correct fittings and hose lengths for GM and Ford of steering boxes and steering racks. All kits feature high pressure.
Concept One offers black AQP hose and PTFE teflon-lined braided stainless steel hose. Both offerings can handle the high pressure requirements, but the AQP hose is much easier to work with than the teflon lined stainless. It's worth noting that Concept One AQP hose is black which blends in to the engine bay better than the blue hose available elsewhere.

Links

Hydroboost Hose Kits

Aluminum Power Steering Reservoirs Standard and Hydroboost

Hydratech Braking Systems

Pro-Touring.com