I replaced my old style vacuum pump (the type with 2 lines and a diaphram) about 20,000 miles ago with a brand new one (says made in Spain). Recently the vacuum system failed on the new pump so I took it apart to locate the problem.

With the pump removed from the engine, I could hear a hissing sound on the engine side of the pump when actuating the diaphram plunger. I thought this was the result of a torn diaphram. Not so. The bolt that attaches the diaphram to the plunger rod had worked itself loose and threaded itself forward toward the valve chamber. In doing so, it actually popped a 3/8" hole into the aluminum valve chamber.

I replaced the broken valve chamber with another one and re-attached the diaphram and plunger bolt using blue Locktite. All is well now.

Maybe they ran out of Locktite at the pump assembly line or something. Seems like a poor assembly job to me anyway.

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Gary

1979 300D