Top Hydro-Vac Questions

  • My brake pedal is hard all the time. Should I replace the hydro-vac?

     Make sure to check the vacuum supply. It should be at least 18-22 inches of vacuum. Also check for contamination in the system, frozen calipers, frozen wheel cylinders, or a restriction that can cause a hard pedal.
  • I replaced the hydro-vac and my pedal still drops to the floor. What’s wrong?

    This is a hydraulic system failure, not a booster defect. Several things may be causing this condition: Air in the system, material friction compression, brake hoses expanding, or defective drums. To diagnose the system begin by gently pinching off the rubber hoses closest to the master cylinder. Release one brake hose at a time. Press the brake pedal. If the pedal is firm and hard, move to the next circuit. Repeat the process until the circuit containing the defective component is located (the pedal will be soft or sinking). Replace defective components as necessary. Also bleed the system thoroughly.
  • I hear a loud hissing coming from the unit and have a hard brake pedal. What’s wrong?

    Check the vacuum connectors and hoses for leaks. If none are found, the diaphragm has ruptured and is leaking. Replace the unit.
  • I replaced my hydro-vac unit several times because it has failed. What is causing this problem?

    The most likely cause of the repeat failures is gasoline contamination from the engine. Check engine for a rich running condition. Correct as necessary.
  • I just replaced the hydro-vac and now my brakes lock up. What’s wrong?

    Check the following: brake fluid for contamination, proper master cylinder push rod adjustment, frozen wheel cylinders or calipers, restricted hose(s). If OK, water is present in the brake fluid causing it to expand and apply pressure to the brake assemblies. Flush the system.
  • The installation instructions state that oil must be added to the diaphragm. What is the correct fluid to use?

    Only units with leather diaphragms need oil added to the unit upon initial installation. Install two to three ounces of hydraulic fluid into the diaphragm via the vacuum fitting.
  • How can I tell a single from a dual diaphragm unit?

    Single units have only one vacuum chamber and duals have two diaphragms in tandem.

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