QuestionShould I be able to pull a vacuum on my power booster when it is removed from the car and on my work bench? I have two rebuilt units, but I cannot pull a vacuum on either one...on or off the car...any advice? thanks...
AnswerYes, you should be able to operate the booster off the car, or on it, by attaching a vacuum source to the vacuum connection. However, it takes quite a bit of volume and a good strong pull to get a good vacuum, so depending on what you are using to produce the vacuum it might not be enough to get the booster to work. If you have a vacuum gauge, tee it into the line to see if you are getting at least 15 In. Hg. of vacuum - more is better - your car's intake manifold will pull about 20 In of vacuum if it is in good shape, at idle.
If you cannot develop vacuum by using the car's intake manifold, and the engine is healthy, something isn't right - if you cannot find a leak, and nothing is pushing on the brake pedal linkage, I'd say your boosters are bad. That is very unlikely, however, because any reputable booster rebuilder would have bench tested it.
If you are trying to do this with a vacuum cleaner, it probably isn't generating enough of a vacuum to operate the booster. Try doing the same thing by connecting to the intake manifold and starting the engine.
If you are using an AC service type vacuum pump, it will not generate enough volume to do this unless you tee in a large vacuum reservoir in the line - a reserve tank, in other words, and let the pump run a long time to build up 20 inches or so of vacuum before you try the booster.
Dick
