Gimme a Boost: How to Build an Inexpensive Power Brake Vacuum Booster

This is Doug Eisberg’s engine compartment just before the power brake booster pump swap. We’ll show you how an enterprising pair of San Diego car guys fabricated a cool power brake booster system that really works.

This is Doug Eisberg’s engine compartment just before the power brake booster pump swap. We’ll show you how an enterprising pair of San Diego car guys fabricated a cool power brake booster system that really works.

Words By: Jeff Smith

Photos By: Doug Eisberg, Eric Rosendahl, Jeff Smith

What’s the first duo that pops into your head? The great ones will always be great — peanut butter & jelly, Abbott & Costello, and perhaps Captain Kirk and Mr. Spock. A far less effective duo for a street car is a big cam and power brakes. High overlap camshafts combined with power brakes often create a hard pedal that makes it difficult to stop at slow speeds, where the engine vacuum just can’t supply the needed boost to make the power brakes effective.

Eric Rosendahl and his long-time compatriot, Doug Eisberg, shared this common affliction. Doug’s 496c.i. Rat-motored Nova was built as a Q-ship — a poseur — masquerading as a stock 396 Nova. Eric’s approach was to dump the wimpy small-block in his ′66 El Camino in favor of a 468 iron-headed Rat that makes 580-plus lb-ft of torque. Eric’s name may sound familiar; we used his Rat as our test mule for installing a hydraulic roller cam (“Let It Roll” PPN) followed by a comparison of a trio of hydraulic roller cams (“The Duration Game” PPN). Both of these previous stories can be found at powerperformancenews.com.

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This is Eric’s diagram of how they plumbed the vacuum lines for Doug’s Nova. Because he wanted the make this install as stealthy as possible, it uses a near invisible T-fitting between the engine connection and the vacuum booster, using five check valves total. Compare this to Eric’s El Camino revised routing diagram that employs one fewer check valve for simplicity.

Both cars had similar brake performance issues. The first application of the brake pedal produced acceptable braking performance. But at low vehicle speeds, if the brake pedal was applied more than twice in quick succession with the engine near idle in gear (both cars are automatics), the pedal effort quickly deteriorated into what could easily be a dangerous situation should a panic stop be required.

While resorting to manual brakes was an option, both decided that what was really needed was additional vacuum assist during low speed situations. Eric performed hours of research and discovered a GM factory vacuum pump for a 2011 V6 Cadillac CTS that was designed to perform this exact task. Even better, the vacuum pump was affordable at well under $140 from either RockAuto or Summit Racing. After coming up with a suitable test plan, Doug bought this pump, and the pair decided to test it on Doug’s Nova.

The specs we found from Hella do not recommend this product to be used as a primary source of vacuum for a power brake unit, although it is the exact same pump used by Cadillac. In this case, the pump is not the sole source of vacuum assist. The guys are using this pump to supplement engine vacuum supplied to the vacuum reservoir. The specs on the pump offer an operating lifespan of 1,200 hours at 1 million cycles, operating at a draw of less than 15 amps when supplied with at least 13 volts. This sounded like sufficient durability. The question would be how it would work on the street.

Besides a pump, the plan demanded other assorted components. From a power standpoint, the pump would require a 30-amp relay to supply power. Next, a specific vacuum sensor switch would be required to sense a low vacuum to trigger the pump. A crude alternative would be to operate the pump any time the brake light switch was engaged, but this would place a much greater demand on the pump than necessary, especially with the addition of a vacuum reservoir. Eric found the vacuum switch through Stainless Steel Brakes at Summit Racing for less than $35.

Doug’s engine idles with between 9 and 10 inches Hg of manifold vacuum in gear, so this application would ask the pump to increase the vacuum to roughly 18 inches Hg. By adding the vacuum reservoir, this does not increase the vacuum, but does increase the volume as a safety measure for greater capacity than just the small volume found in the booster itself.

Eric also reasoned this system might ultimately be safer than other boosted systems. In a typical engine-fed power brake system, if the engine were to stall, the driver would have one to perhaps two brake-assists before the pedal effort would drastically increase. With a hydro-boost system, if the engine stalled, the same effect would be generated. With this electric motor vacuum boost system, if the engine dies but the ignition power remains on, the electric pump will still supply vacuum assist to the brake pedal, as long as the battery offers sufficient voltage.

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This is a simplified drawing of the wiring for the relay. Be aware the terminals on an actual relay will be positioned differently than this drawing, but the connections are correct. Also, be sure to ground the pressure switch body as it is the ground circuit for the relay that closes the circuit and turns the pump off.

Armed with this approach, the guys decided to first test the AC Delco Caddy pump on Doug’s Nova by temporarily bolting it to a wood base to the driver side fender and plumbing it in between the engine and the power brake booster. This initial test was run without the added volume of the reservoir, but the results were impressive enough that they then decided to build a permanent mount for the pump and reservoir.

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This is Eric’s 468c.i. big-block El Camino engine compartment that will be the next install. He plans to mount his pump and reservoir in the same location but will plumb his system slightly different, as shown in the next diagram.

As we mentioned earlier, Doug’s thing is to keep his Nova as stock-looking as possible. So the pair built an aluminum bracket to mount the pump and the reservoir underneath the driver front fender and above the inner fender well, using longer bolts from the hood hinge as studs to mount the bracket. They oriented the pump horizontally, both for clearance and also to minimize the load on the pump, although Cadillac locates the pump vertically with pump end up. They also bent lengths of 3/8-inch tubing and connected the lines with vacuum hose and clamps.

With the system in place, they were also concerned with noise, but that also turned out well. With the pump in place and running, they used a meter to measure the sound at 64 dB from two feet away with the hood closed. This is equivalent to normal conversation in a restaurant. So, yes you can hear it when Doug first turns the ignition on, but once that gnarly big-block fires up, the noise is completely masked.

This is Eric’s diagram for the plumbing for his vacuum pump system in his El Camino.

This is Eric’s diagram for the plumbing for his vacuum pump system in his El Camino.

Test drives with the Nova quickly revealed Doug now has brakes like he hasn’t experienced in years. He can apply the brake pedal multiple times in quick succession without an increase in pedal effort, and the car now stops in a much shorter distance at low speeds with normal pedal effort.  At this point, Doug has roughly 300 miles on the system, but he is thrilled with the package and now, Eric is assembling the parts to perform his version of this system on his big-block El Camino.

This is a comparison of the engine manifold vacuum generated by Doug’s Nova, as shown on the vacuum gauge on the left at slightly above 9 inches Hg. The vacuum gauge on the right shows the Cadillac pump has increased the vacuum for the booster up to around 17 inches on its way to 18 inches Hg. Note we’re reading the inside scale — inches of manifold vacuum.

This is a comparison of the engine manifold vacuum generated by Doug’s Nova, as shown on the vacuum gauge on the left at slightly above 9 inches Hg. The vacuum gauge on the right shows the Cadillac pump has increased the vacuum for the booster up to around 17 inches on its way to 18 inches Hg. Note we’re reading the inside scale — inches of manifold vacuum.

So, if your older supercar is suffering from the high pedal effort from power brakes, due to low engine vacuum at low speeds, this just might be a way to make the car both more fun to drive and safer at the same time. And you can do it all for $250.

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Sources: RockAuto; rockauto.com; Summit Racing, summitracing.com

About the author

Jeff Smith

Jeff Smith, a 35-year veteran of automotive journalism, comes to Power Automedia after serving as the senior technical editor at Car Craft magazine. An Iowa native, Smith served a variety of roles at Car Craft before moving to the senior editor role at Hot Rod and Chevy High Performance, and ultimately returning to Car Craft. An accomplished engine builder and technical expert, he will focus on the tech-heavy content that is the foundation of EngineLabs.
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