I'm out of town.. visiting and on someone else's computer so I'm writing very quickly. I don't have my Haynes book with me, but the test I mentioned is for the Vaccuum Brake Booster.. not the vaccuum pump as I may have led you to believe. In any event if you could get your hands on a Haynes Manual then it has some steps to follow. Keep us posted.

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Nello Tare

1982 300D (266,001 mi.) looking and running great

Previously owned:
1976 450 SLC
1983 300D
1976 300D
also
1982 Jaguar XJ6 (loved, but gone)