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JeepEV: Electric Vehicle Conversion Project
Power Brakes


     The Jeep's power brake system was "boosted" by a typical vacuum booster unit that worked off the vacuum of the Internal Combustion Engine. With the I.C.E. gone, an electric vacuum pump will provide the neccesary vacuum to operate not only the brake booster, but also the climate control system ducts. The pump itself is made by Gast, and is a self contained 12 volt pump. There is also a vacuum switch, in this case made by Square D, utilized in the system. The switch turns off the pump once around 23" hg vacuum is pulled. If the vacuum falls below ~15" hg (such as the brake pedal being depressed), the switch re-energizes the pump. Good Plan!

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The Vacuum Pump and Vacuum Switch.


     Before I knew where I would end up mounting the vacuum system components, I temporarily mounted the vacuum pump and switch to the front driver's side of the engine compartment. I hooked everything up and it worked, just as I suspected!

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The Vacuum pump and switch are temporarily installed at the
driver's side front fender.


     Once the front battery racks were made, I soon realized just how much free space there was under the battery racks, especially battery rack #2. Luckily, free space + solid metal nearby = an easy way to weld and mount things. First, I bought some 1/8" flat steel. Next I cut and welded pieces of it to the under side of the battery rack's lower tray to provide mounts. For the vacuum pump, I welded two long pieces and one short tab to the bottom of the tray. Next, I drilled three holes to match the three pre-threaded holes in the bottom of the vacuum pump.

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The Vacuum pump is mounted via three holes to flat steel
welded to the underside of battery rack #2.


     The vacuum switch was attached to the bottom of battery rack #2 in the same way as the vacuum pump, and right next to it. It only required one piece of flat steel, and mounted to it using two bolts.

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The Vacuum switch is also mounted to a piece of flat steel
welded to the underside of battery rack #2.


     Another necessary component of the vacuum system is a vacuum reservoir. The vacuum reservoir stores vacuum for use, so that the vacuum pump doesn't need to turn on for every little use of vacuum, but instead can run less frequently. Most vacuum reservoirs are made out of plastic. I decided to make a vacuum reservoir for the Jeep out of lengths of 2" Class 200 PVC pipe. I chose Class 200 PVC because Class 200 has thinner walls than Schedule 40 PVC, and thus has more volume for than an equally sized length of schedule 40 PVC.

     I bought 2" blank cap ends to close off the sections of PVC I would use as the vacuum reservoir. I then drilled holes in each cap end to accept a threaded metal barb fitting for the vacuum hoses to attach to. The first tube of the vacuum reservoir has one cap with a 5/16" Inner diameter hose barb (input) and one cap with a 1/4" barb (output). The second tube of the reservoir has both caps with a 1/4" barb in them. The last tube of the vacuum reservoir has a 1/4" barb in one cap (input), and both a 1/8" and a 5/16" barb in the other cap (output). The metal barb fittings are screwed in tightly. I then put silicon around them to make a vacuum tight seal.

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Metal barb fittings which are threaded on one side are
screwed into 6 2" PVC caps for the vacuum reservoir.


     Once the caps were made, it was time to attach them to the three lengths of 2" diameter PVC I had cut. I used the purple primer to clean the pipe and caps. Then glued them together with the blue (quick drying) PVC cement. The last step was I spray painted the vacuum reservoirs white to hide the lovely combonation of purple and blue stains which had been left by the PVC chemicals. I then connected 1/4" hose between each of the three sections to form one big reservoir, and installed the new vacuum reservoir underneath front battery tray #2, between the vacuum switch and power steering pump.

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The ends are glued to the pipes, and the vacuum reservoir is installed to the underside of battery tray #2



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