It’s not uncommon for a street rod to run a radical camshaft, since big power is what rodding is all about. Problem is, though, when you’re ramming around town, you may enounter a problem with slowing down if your street rod relies on a factory-style, vacuum-powered brake assist unit. This system can present a substantial problem with braking at low engine rpm, due to an inadequate vacuum supply to the brake booster because of the cam’s extreme lobe shape. On top of that, other areas of the car, such as automatic transmissions and A/C systems, also need vacuum, which then takes it away from the brake system.
A quick remedy for this scenario is to use a product that has been commonly available as a general automotive service part since 1974. This proven approach is currently found on a wide range of new production vehicles, everything from V8 Mustangs to Chevy pickups. As such, it has undergone rigorous testing by OE manufacturers to insure proper operations and reliable operation.
Called a Hydroboost, this hydraulic brake assist relies on hydraulic pressure from the power steering pump to provide far more brake assist power. For comparison, a standard vacuum unit normally can produce only 450 psi, while a Hydroboost system from Power Brake Service generates 1200 to 2000 psi to the calipers.
If your street rod already has a master cylinder (assuming it has power steering to begin with, which is required to add the Hydroboost), in most cases it can be used, as long as it is in proper operating condition. If your master cylinder is more than ten years old, though, or shows signs of aging and wear, it should be replaced.
A sano-looking engine bay is a big issue for most street rods, so the PBS Hydroboost is handcrafted to a high level of visual quality. The units can be anodized or finished with a chemical-resistant paint. The line sets use Aeroquip TFE spec materials, with adjustable aluminum line separators featured in most applications.
If spacing is an issue, as is common with many older body styles, the Hydroboost saves room over a typical vacuum brake booster, usually about four inches more spacing for tall valve covers, in comparison to the average vacuum brake booster. Of course, the space savings will vary from vehicle to vehicle, and if necessary, the unit can be mounted remotely in the chassis, as shown in the photos.
Some older street rod setups may have drum brakes up front, which is not recommended for a Hydroboost system. In this case, you’ll also need to add a front disc brake conversion kit, available from a number of aftermarket companies. While most street rodders think first about getting the “go” before the “slow”, updating your stoppers with a modern braking system is a smart addition to your project.
Power Brake Service
The bottle on the side of most hydraulic brake assist units is called an accumulator or nitrogen reserve. It stores up hydraulic power steering pressure in the event of an engine-stall condition in order to provide reserve brake assist power for up to three full-power applications of the brake (similar to how a vacuum booster functions in an engine-stall condition). Once you have depleted all of the stored pressure, the brakes will no longer have power assist and will be manual in their operations. The minute you start the vehicle back up again, the accumulator gets filled back up again with pressurized hydraulic fluid.
Anodizing or chemical-resistant paint can be used on the Hydroboost to color-coordinate the system.
These fittings are for the fluid output (right) and return line (left).
On the opposite side is the inlet fitting for hydraulic fluid from the power steering pump.
Shown here is the spring retainer pushes the piston back into its release position. Other interior components include a power piston, spool valve, and hydraulic reaction control for pedal feel.
Here’s a typical installation on a 350 Chevy using a Wilwood reservoir and braided lines to the power steering pump. Installation requires removing the existing high-pressure power steering line between the pump and the steering box or control valve. A replacement line goes from the pump to the assist unit, then another line from the assist unit to the original steering connection. This system piggybacks the power steering system, using the fluid pressures, on demand only, to provide brake assist, without a disruption of normal operations.
On this big-block Ford, the Hydroboost required a slightly rotated mounting for clearance of other components.
If there’s not enough room in the engine bay, the Hydroboost can be mounted remotely, in this case on the frame rail next to the transmission.