![]() ![]() Off-road trucks and buggies have adopted Hydro-boost because it allows drivers to control low-speed crawling with oversized tires. Hydro-boost works the same no matter the throttle position or engine load, unlike vacuum. How much boost you get is dependent on how much pressure the power steering pump puts out, but more than 1000 pounds is typical. Of course, you need a power steering pump to make it work, but it is just a matter of plumbing if you already have power steering. Hydro-boost (Bendix's name for the system when invented in 1973) uses pressurized fluid from the power steering pump instead of engine vacuum to amplify your leg effort. GM used hydraulic brake boosters between the master cylinder and firewall on many 3/4 and 1-ton trucks (and the Buick Grand National), and Ford used one on the 1999-2004 Mustang because of a lack of space. These units can be found in the junkyards or purchased new from aftermarket suppliers. ![]() Hydro-boostĪnother solution is to use a hydraulic assist, or Hydro-boost, system. There are also electric vacuum pumps available. Some vehicles used a motor-driven vacuum pump mounted to the rear of the alternator from the factory. If the only issue is a lack of sufficient vacuum from the engine, a vacuum pump may be the simplest solution. A dual-diaphragm booster doubles the area and the boost.īut you need vacuum to use any booster, and you need room to mount it. The math works like this, 4” x 4” x 3.14 = 50.24 sq. inches x 8 psi = 307.7 pounds of force.Ī larger diameter booster gives more boost moving up to an 8-inch size adds an extra 100-pounds. If it has been a while since high school geometry, that means 3.14 x half the diameter x half the diameter. The surface area of a circle is found with the formula of A = π x r2 (we'll pretend the dead area in the center of the diaphragm with the pushrod isn't there). To get that number, multiply the diaphragm area in square inches by 8 psi (ignore the negative nature of the number). So if you have -8 psi on one side of a small 7-inch diameter vacuum diaphragm booster (as small as they come) and regular atmosphere on the other, it adds about 300 pounds of assist when you hit the pedal. A mildly tuned engine with 16-inches of vacuum at idle translates to about -8 psi (actually 7.86, this is complicated to explain, so Google the conversion). Manual Brakesįiguring how much assistance you get from a vacuum booster is simple math. Other times, the radical cam timing of a high output motor doesn't create enough vacuum to power a traditional vacuum booster. For example, often shoehorning a big motor into a small engine compartment leaves no room for a vacuum booster on the firewall, even with an angled (Ford Bronco) or offset (many vintage vehicles) mounting bracket. Manual Brakesįor some projects, the question of power assist or manual brakes is merely a personal preference, but the choice is forced on you for others. Get them both right, and even with manual brakes, you'll be able to stop your car or truck on the proverbial dime. Both amplify your muscle effort to help the car stop, with or without a power booster. The pedal ratio is the relation of the pedal pad, master cylinder pushrod, and brake pedal pivot. The hydraulic ratio relates the master cylinder piston size to the piston area in the calipers. When planning a performance manual brake system, such as for a race car, muscle car or street rod, getting the pedal and hydraulic ratio correct is even more critical. ![]() If you are just planning your build, now is the time to decide if you are going to go with boosted brakes or not. While Wilwood prefers manual brake systems, a holdover from our racing roots, our calipers and master cylinders work equally well for power or manual brakes. Many popular hobby cars come from the era when power brakes were an extra-cost option, and drum brakes were the norm. ![]()
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