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Hydrovac newbie question

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  • Brakes: Hydrovac newbie question

    Guys - I bought a rebuilt (Boursin) hydrovac on Ebarf that will fit nicely under the hood of my '58 Champion sedan and, I hope, provide a few more PSI to my front Turner discs.
    I'm in the process of getting the necessary fittings and the kindly gentleman at the brake & clutch store said I should have a firm brake pedal before starting the car and introducing vacuum to the unit. He said to bleed it out thoroughly then start the car. I will take his advice and certainly consider more from anyone who has experience with these. I've added power boosters in the past, but only when it's a firewall mounted M/C and the fit is easily (relatively speaking) behind the master. This is new and exciting territory for me. Thanks!

  • #2
    The hydro-vac is basically a second boosted master cylinder. The first most familiar master cylinder under the floor basically controls the vacuum booster valve which in turn the vacuum piston pushes on a second, built in slave master cylinder on the unit.
    Most overlooked is that the slave cylinder also has the same drawback of often neglected maintenance. They also collect sludge, and will rust the iron bores just like any wheel cylinder. So they need to be flushed, and bled with fresh fluid every three years just like any other system using non dot 5 fluid.
    You bleed the system like this: bleed the master cylinder first, then the next point would also be the highest point. That would be the top bleed valve of the hydro-vac. Then the slave cylinder bleed fitting on the end of the cast iron hydro-vac cap. Then the longest furthest away brake cylinder....which would be the right rear, Then left rear, then right front, then finally left front.
    Bez Auto Alchemy

    "Don't believe every internet quote" Abe Lincoln


    • #3
      Super helpful! Thank you!