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Power Brake Booster Vacuum Reservoir

By Ralph Granchelli

All of the technical information and product information posted on this website is offered as general information and is not recommended, endorsed, guaranteed or presented as professional technical information.  It is recommended that you seek professional help for the repair or maintenance of your car.  Improper self-maintenance or repair of your car can result in serious injury and or death.  Use of this information is done at your own risk.   

After installing a large lift & duration cam, either a roller or flat tappet, with high performance lifters, you will most likely find that your engine does not produce the amount of vacuum it used to.

Most power brake boosters are vacuum operated devices requiring approximately a minimum of 17 inches of vacuum to operate. You can check the amount of vacuum your engine makes with a vacuum gauge. If less than the required amount of vacuum is made, you will need at a minimum a vacuum reservoir. Many engines will make enough vacuum to operate the booster under some operating conditions. This reservoir works by storing the peak vacuum in the reservoir when it is made. If this set up does not produce enough vacuum to run your booster, you will have to use a vacuum pump to make the brake booster work. The auxiliary pump will make from 18 to 20” of vacuum. Some pumps can be connected to the booster directly. Alternatively you can the pump to pull down the reservoir and block off the vacuum line to the engine as you do not want the pump to pull down the engine vacuum line.

You will need the following materials:  

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The bracket for the reservoir will be fabricated from the piece of aluminum. First polish the piece of aluminum using a buffing wheel and white compound. Wear goggles, gloves and a dust mask.

One end of the bracket will attach on the outside bolt of the booster to master cylinder. It will then parallel the master cylinder, making a 90 degree angle pointing down. I bolted it to the proportioning valve. 

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Assemble the bottle. On one end there is a single plug. Teflon tape the plug and screw it  in tight. We want no leaks as it will affect brake performance.

Assemble the other end of the bottle. Teflon tape the gauge and install. Teflon tape the 90 degree 3/8 hose barb and install. Install the grommet. Install the check valve into the grommet.

Where the vacuum hose from the engine comes up from below through the grommet, push the ½” hose barb side of the adaptor into the hose and clamp. Run the 5/16 side using black vacuum hose to the check valve in the center of the reservoir, clamp all connections. Run the 5/16” vacuum line from the 90 degree hose bard on the reservoir to the brake booster check valve. Clamp all connections.

Start the car and check the vacuum. Rev the engine and observe the peak vacuum to determine if there is enough for your application.

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The Finished Application

Bleed your brakes at least once per year or earlier if the color starts to change. I evacuate the old fluid with a power bleeder, then final bleed the system the old way. Use either an assistant, or do it with a one man bleeder bottle. Starting with the wheel cylinder the furthest away from the master, bleed in this order, RR.LR,RF,LF. I use Castrol GTLMA, DOT4 fluid.

If you have other brake problems, please refer to this link@ MP brakes:

The above list is a fine reference list of things to check. However to zero in on the problem I use the SSBC A1704 sure stop pressure gauge to diagnose brake problems. You simply pull the bleeder, use the correct adaptor and apply the brakes and take a pressure reading. By taking 4 wheel readings you should be able to determine the root cause.

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This article is provided for reference only. Failure of your brakes to operate can result in death and property damage. Please see a certified brake specialist to assist you in resolving your specific brake needs.