One of the greatest causes of failure of this type of unit is gasoline getting into the unit. Before replacing the old unit, check it for gasoline odor. If gas odor is present, then steps must be taken to protect the new unit, or it to will fail, sometimes in just a day or two!

See Installation Details Below

Most trucks equipped with Bendix Hydrovac or Midland Hypower boosters are built with a check valve mounted high on the fire wall, so that raw gas and vapors will not get into the power unit. If this has been changed, or if the truck was built without it, so that the vacuum line from the manifold to the unit goes down directly to the unit instead of first going UP and then back down, it must be changed before replacing the unit.

If raw gas or gas fumes reach the rubber diaphragm, it will deteriorate quickly. On cab-over installations with no fire wall, it may be necessary to make a bracket on top of the air filter, so that the vacuum line can go up for eight or 10 inches, and then down to the power unit.

The vacuum line from the manifold to the unit should first go to a check valve that has been checked to be sure it's working properly. The vacuum line should then be routed directly the booster.